Well firstly you'd probably get more answers to it in either the hardware or beginners forum, but I'll bite anyway.

In terms of hardware, your PC spec is v similar to mine except I have 3gb ram and only an 8600 GFX card. I run 5 wow's passably on this, so if you are for e.g. doing 4 on that pc and 1 on another, you'll be getting pretty good performance.

In terms of group setup, I strongly advise you once you've got all the accounts, to make up your preferred team and give them a shot to 20-30 or so, it doesn't take too long, and you'll have a great flavour of it by then.

I personally started out 4 boxing a druid, 2 locks and a shammy, since then they are on the shelf as I 4 box 4 shammies (to 61 so far).

Welcome to the forums and good luck with it.