Hey there, Tesh. I know that it can this can be pretty intimidating for you after a 10 year haitus. I’ll do my best to help you and offer some related advice. With that in mind, let’s start at the beginning.
SOFTWARE:
Let me warn you of something in advance. By and large, perpetual licenses are a thing of the past as developers have opted to milk the cash cow ad infinitum. There are alternatives, but I’ll get to those in a moment.
You said that you were a Maya & ZBrush user back in the day. Those apps are both still relevant and industry standard. For the most part, they still dominate the job scene. Before I digress and with that in mind, if you still have a legal license & valid Pixologic login, upgrading to the current version of ZBrush (v2021) should still probably be free. (I’ve been getting free upgrades for 12 or 13 years now. It’s just Pixologic’s way.) Otherwise, it’ll cost you about $900 for a perpetual license or $40/month for a subscription.
Maya is still plenty expensive. Now a subscription only application, it’ll set you back $205/month, $1,215/yr, or $3,282/3yr. HOWEVER, in order to keep up with recent trends, they also now offer a Maya Indie license for about $265/yr. The only difference is, being an Indie license, you cannot earn more than $100k/yr using it. Other than that, the program is exactly the same as the regular studio Maya. No watermarks or anything.
You’ll very likely also need a copy of Photoshop. Again, no perpetual licenses. Subscriptions only. Mercifully, if all you need is Photoshop and no other Adobe app, you can snag it for as low as $10/month.
Here’s my advice. You’ve got a 3 year old kid. You’ll probably want to keep as much of you hard earned cash as possible. Instead of the above apps, I’d recommend the following.
INSTEAD OF MAYA… Why not pick Blender v2.9x. Blender has come a VERY long way since you last saw it 10 years ago. It is still 100% free as in beer and a force to behold. The UI has been significantly overhauled as to make it more intuitive and in line with other apps like Maya or Cinema4D. It has also grown to include a very robust feature set that is not only competitive, but even superior in certain areas. While it is not (yet) the industry standard, Blender has begun to gain some real traction among industry pros and smaller studios in recent years. The bundled rendering engines are top notch too. Blender is a highly competitive piece of software.
INSTEAD OF ZBRUSH… Again, go with Blender. Yes. ZBrush IS the de facto standard when it comes to sculpting. It is still crazy fast and able to handle an obscene number of polys. HOWEVER, Blender’s native sculpting tools are so powerful that it has become a legitimate alternative for sculpts of 25mil polys or less. Recent tweets by the developer working on the sculpting tools indicate that there’s also a massive speed increase for HD meshes on the horizon too. Based on the posted video, sculpt speed looks to be in for a good 5x-10x bump. It’s safe to say that, even now, you can create some amazing looking and highly detailed sculpts using Blender alone.
INSTEAD OF PHOTOSHOP… I’d probably go with Affinity Photo. Yes. Photoshop is only $10/month, which even a guy with a 3yo can afford. Still, $10 is $10. If you can save $120/yr, why not? Affinity Photo is offered for a one time $50 price, is a true perpetual license, & doesn’t require any sort of online activation. Feature for feature, Photoshop still holds the advantage. However, out of all of the PS alternatives, Affinity Photo offers the most Photoshop-like experience and feature set. It’d rate it somewhere below PS proper, but miles ahead of the opensource Gimp - which many indies and hobbyists swear by. Serif, makers of Affinity Photo, also offer an Adobe Illustrator Alternative for vector graphics called Affinity Designer. Also a $50 one time cost. Also perpetual. Also very good.
There’s something else you need to be aware of. While it’s still totally possible to make textures in a 2D app like Photoshop or Affinity Photo, most texture artists these days tend to paint theirs in a real-time app such as Substance Painter. Substance Painter allows you to paint directly onto the mesh and across multiple texture layers. Substance Painter (and Designer) came onto the scene just about as you were taking a break from things 10 years ago.
Substance used to be independently owned by Allegorithmic, but has been recently been bought by Adobe about a year or two ago. As such, predictably, they’ve gone from a perpetual license to a subscription model. Subscribing to Adobe’s Substance suite will set you back about $20/month. HOWEVER, what they don’t tell you is that you can actually still get a perpetual indie license from Steam for about $150. For that price, you get about 12 months of updates. The Steam version of Substance Painter will still work well after your 12 months of support ends though. Still, $150 is still a bit of cash for a father of a 3yo. I get it.
INSTEAD OF SUBSTANCE… Use Blender in combination with ArmorPaint. Yes. You can actually paint in 3D with Blender. I told you. Blender is a powerhouse. For 3D painting, Substance is still superior. However, it’s 100% possible to paint high quality textures in Blender. There are even a number of very cheap plugins to add extra 3D paint features and make your life easier. If Blender isn’t enough or you demand a dedicated 3D paint app, I’d direct you to ArmorPaint. It’s an open source alternative to Substance Painter that’s fairly new to the scene. It’s still evolving and very much a WIP. However, it’s free… as long as you can compile the source code yourself. If you can’t… Dont worry. You can get a pre-compiled version for just under $20 through Gumroad. (https://gumroad.com/l/armorpaint) The updates are free and the app is perpetual.
To answer your questions…
Your PC needs all depend on how complex you want your scenes to be. It’s that simple.
I’m a PC user and can’t speak directly on your Mac Pro. However, Blender’s minimum spec is very forgiving. A pimped out screamer of a PC will always get the best possible performance and handle huge scenes. However, according to the Blender Foundation, any computer made within the past 10 years should suffice. Just make sure that you’ve got at least 4GB RAM and are using an OS that is no older than macOS 10.13 or Windows 7.
I currently use Blender on a 14-core i9 with 64GB RAM, 18.5TB HDD, 4K monitor, & 1080ti 11GB GeForce. … HOWEVER … My 8yo neice started to learn Blender over the summer while in quarantine on a 3 year old 4-core Intel i5 with just 4GB RAM. I can handle much bigger and busier scenes, but her PC spec is still powerful enough to do some really good stuff with. Just beware. Older systems will, unsuprisingly, render slower than more modern systems.
That said, you don’t need a super PC to do 3D. You don’t. To put it another way, if you can still play games at low or medium settings, you should be fine. If your 4yo laptop can play the equally old “Deus Ex: Mankind Divided” (2016) or even older GTA V (2013) at any level of quality (even low), your 4yo laptop should be more than powerful enough to get you back into the CG art game.
At some point, you’ll probably want to upgrade your PC. After all, a 4yo laptop isn’t getting any newer. For now, however, you’re good to go. 100%.
Guru, thy name is YouTube.
It used to be that sites like Digital Tutors (now known as Pluralsight) or Gnomon were #1 source for online training. You could buy some high quality training DVDs and learn just about everything. However, DVDs were never able to keep up with the tech or the demand. As such, most of you tutorials will be streaming.
As a born again newbie, your first stop should be YouTube. The quality of tutorials on there will range from bad to great. You’ll have to do a bit of sifting through the crap to find the gold. However, there IS a lot of gold there if you’re patient. As you might expect, YouTube streamers cover just about every topic you can imagine. ZBrush. Maya. Blender. Photoshop. Concept art. Sculpting. Sketching. ETC ETC ETC
As a Blender artist, I would probably also direct you to Blender Market & Gumroad. The training material there is all $$$, but it’s usually quality stuff. Nothing more expensive than $75. Tutorial range from 36hr+ all encompaing courses to shorter, cheaper 8hr tutorials that will show you how do do stuff like model cars, make real-time hair, sculpt monsters, and so on.
For a good all-in-one tutorial site, you could opt for Udemy. They cover countless topics that include, but extend well beyond 3D. Some people love Udemy. Others hate it. I, personally, have never needed it so I can’t vouche for it though. I do know, however, that you might want to read the individual course reviews before opting in. Some “instructors” are just hacks.
Yeah. Sorry. You’re not getting around it. You could opt for auto UV algorithms if you just want to jump to the painting. However, there’s no substitute for manual UV unwrapping. You’ll get the best results and make the most of your UV space if you do it yourself. For my money, I find Blender’s UV tools to be a tad easier to work with than Maya’s. The results will be comparable though.
Either way, UV unwrapping is a necessary evil. It’s mildly time consuming, but you get used to it after a while. TBH, you’ll find mesh retopology - constructing a well ordered and lower poly mesh from a denser one - to be more tedious. I find it to be a good way to zone out, but some people would rather eat glass. To each his own. 
Yes. Wacom tablets are very much still a thing an aren’t going anywhere anytime soon. People DO create art on MS Surface tablets. However, from my experience, there’s no substitute for a real PC. Having access to a big screen and full sized keyboard is always to your advantage. Surface tablets (and iPads) are still mighty capable for 2D concept art and painting, but I’d stick to a desktop or laptop for “real” CG work.
You don’t have to invest $2K+ on a pricey Wacon Cintiq pen display to get back into the game. I’ve got one and it’s amazing, but you can go MUCH cheaper if you’re just starting out. You can snag a brand new Intuos Pro (small) for about $250 or an equivalent Huion tablet (eg. H610 Pro) for about $50. Both will do the job just about the same.
I would, however, direct you to stay away from the cheaper $50-$90 non-Pro Wacom Intuos tablets. They’re good and do the job, but the button placement is just terrible. Placing those express keys at the top instead of the side is just a pain in the ass. Total recipe for wrist strain. I bought one once, to replace my dead Intous3, and regretted the experience. Penny wise. Dollar foolish.
LINKS LIST:
Blender: http://www.blender.org
ArmorPaint: https://gumroad.com/l/armorpaint
Affinity Photo: https://affinity.serif.com/en-us/photo/
Blender Market: http://www.blendermarket.com
Maya Indie: https://makeanything.autodesk.com/maya-indie
Substance Painter (Steam Perpetual): https://store.steampowered.com/app/1194110/Substance_Painter_2020/
NB: You make no mention of wanting to go pro and make a career change. Maya & ZBrush, as I said, are still the industry standards, but Blender is still very much a viable option for freelance, indie projects, small studios, startups, or hobby work. You can achieve the same exact results in Blender as in Maya for $0. (Re)learning Maya is really only a must if you’re hellbent on working at a studio that requires it. Not hard to (re)learn once you’ve mastered Blender though.
For now, imo, go free. Blender is AMAZING. Seriously. Model. Texture Paint. Animate. Sculpt. Video Edit. Composite. 2D cel-style animation. Fluids. Hair. Smoke/Fire. Cloth. A lot has changed in 10 years. Blender has become a beast. Seriously. A lot of longtime Maya and 3dsmax users have jumped ship and converted to Blender in recent years. If you use it, you’ll understand why. I kid you not.
(Autodesk has become greedy, imo. They ask for a lot, but only put in bare minimum effort. In fact, while Maya has seen a number of strong features in the past 10 years, you might not immediately notice them if you jump back in. With 3dsmax, the changes in that period of time are harder to notice. 3dsmax development slowed to a crawl for good 5 years. It was nearly as inactive as LightWave for a while.)
Take a look at a few indie shorts and highlights of Blender.