I redirected your post here because it’s a broader, non-Painter specific question, and also others in this section of the forum would definitely be interested in this topic.
I wouldn’t worry too much about brand at this point, because usually, unless you’re a highly advanced painter, you won’t be able to benefit much from expensive brands anyway, and acrylics isn’t as diverse in terms of price/quality as oil paints, as oil paints are a lot more complex and fickle. I would personally pick any brand that you see a lot in various local art supply stores, because that means if you end up liking certain colors, you have a higher chance of finding the same brand/colors at any art supply store. For example, just about every store carries Liquitex (like how every store carries Winsor & Newton).
I would pick up a tube of retarder–it helps to prolong the drying time, as acrylic dries insanely fast, and that can be an annoyance. Make sure you follow the warning label’s advice about the mix ratio, or you’ll get cracked paints. You’d probably want an acrylic varnish too–glossy or matte is up to you. I like how easily I can photograph matte surfaces, but I think glossy varnish makes the actual painting appear more “sparkly” and vibrant to the eyes. Maybe photograph the piece before you apply the glossy varnish (if you do use glossy)?
Be very careful about your brushes when painting in acrylic–as acrylic is hell on brushes. What I do is to dip my brushes in the retarder first to get it into the brush roots (that’s the area that gets destroyed easily, as paint collects and dries there), then pick up paint with the brush.
Painting with palette knives can be a lot of fun and very expressive, so you might want to give it a shot.
Get some basic colors to start off with–your primaries and some additional colors. In fact I suggest you start with just the primaries and perhaps add white, black, and that’s it. Do a few practice fun pieces with just those colors (you can mix a very wide range of colors with just those). After you’ve done a few pieces and have decided if you like working with acrylics, then you can add more colors to save you some mixing time and increase color purity/intensity.
A good tip on keeping colors on your palette wet is to use a water spray bottle. Spray your palette periodically to keep the surface of the paint blobs wet, because that’s what dries out first (it’ll form a dried film, and the paint inside would still be wet, but the film will still allow the paint inside to evaporate). Don’t spray so much that you get water running all over–just a few light mists to keep the paint blobs fresh. Also, when not painting or taking a break, spray the paint blobs, then wrap the palette in food wrap (or some other enclosure), and then put them in the fridge. That’s right, the fridge. The lower temperture will keep the paint fresh much longer. Don’t put it the the freezer though–that’s overdoing it.
Always wash your brushes thoroughly after painting. Buy one of those brush cleaner solutions/soaps–they really do work great and contain brush conditioning ingredients you won’t get from typical hand soap (if you do use typical soap, you can use hair conditioner on the brushes afterwards–just keep it in and rinse it out the next time you paint). Don’t kill your brushes while cleaning by being too rough with them, just as long as you get all traces of paint buildup in the brush roots out, you’re ok.
The fat over lean rule isn’t as strict in acrylic painting, as acrylic is a form of plastic resin and polymer, and it is relatively flexible (a bit like firm rubber). But you should still try to do your washes underneath, and then do your thicker painting on top. I love using acrylic as a wash medium because I can layer as much as I want since once dried you can’t destroy the already painted surface again like you would with watercolor. As a thick painting medium I don’t like it nearly as much as oils though, as oils is very buttery and smooth (but some find that much harder to paint with since you’d need excellent control).
But I have been recently getting interested in trying out Acrylics which I have never used traditional but always use in Painter IX.