I don’t know where you heard that, but “a lot” isn’t true. Very few engines use the GPU, and those that do are normally not the “animation” centric ones.
If that’s the case, should I get less powerful CPU and spend more money on multi-GPU ?
Find a balance of both.
Should I get Geforce or Quadro?
Search the forums, it got asked a million times
Also, I guess i7 or Xeon already discussed many times on this forum. I guess it’s mainly depend on budget.
Yeah, it’s been discussed many times, so why not read those threads? 
No, it’s not only dependent on budget, XEONs have years ago evolved fully down the computational centre path.
For workstation type uses top tier i7s often perform on par or better at many tasks, and if power requirements and amount of licensed nodes are not a concern, very often a spare i7 renderbox + the workstation will do better than an equally (or more) expensive dual xeon used as both, and allow both at desk work and offline work at the same time.
I’m looking to spend about $4000 for the PC itself not including Monitors.
Depending on country and other things 4000$ might be excessive without the monitors, but then if you buy the absolute most expensive CPU budget goes fast.
For workstation use with Maya and a rendering engine of your choice, with that kind of budget, best i7 you can find, a titan, 32GB of ram, a large SSD for system/apps and a couple striped 7200rpm drives for storage will get you some of the best performance you can buy right now.
It will also be a colossal waste of money with the 7xx gen not too far away and with the next gen of CPUs/chipsets only a few months away, but then bleeding edge top hardware at the end of a generational cycle almost always is a waste of money.
