I was running 11 clients on a crap computer I got from Staples (low settings etc). with 8gb of ram. 8gb will be fine for running 3 clients.. more than enough. About the video card, I don't know a lot about what to get. My friend suggested a AMD 7770 for $160 on NewEgg and it's been a beast! The card I was 11-boxing with was $100 when I got it a year ago. Again, almost anything you get will be somewhat of an overkill.