There isn’t a straight forward answer.
Firstly, far as I’m aware you can only run 2 Kinects from one machine, tracking 2 people. If you could get them working on your Mac, OSC to MAX MSP shouldn’t be a worry.
Secondly, yeah, you want them sending data into different parts of you motherboard to be on the safe side. Its churning through a lot of data.
Thirdly, while your patch won’t be graphics heavy, you’ll want to use a quick machine for keeping the data a-flowing if you’re going to run Ableton/MSP on the same rig. You may be able to do the whole thing on vvvv with the help of the new Audio Pack?
Finally, get the best machine you can afford. If or when you decide to go grfik, have something you can rely on in most eventualities.
So without much further ado, I invite you to take a look at this useful thread:
HNY