One thing I've found that makes the one machine optimal over the five machine route (which I have done in the past) is to make sure to have two monitors. It's almost a must. My 27" Asus was only about 300 bucks on newegg and beside it I just run a 21" that is off an older Dell machine. That way you can put four toons on the smaller monitor and your main toon on your main monitor.

I also have used both Keyclone and ISBoxer from Lavishsoft.com and though it really took some getting used to how poweful ISBoxer is, now I prefer it and use it both for WOW and RIFT.

Good luck.