3 locks isn't the ideal CC due to no reliable control over a mob, but you'd have 4 aoe fears if you pull back far enough, and 3 VWs can occupy a mob for long enough imo. As for focusing on the different classes, if you let the warrior go in, grab all the mobs (apart from the VW tanked ones) and just heal him, then load up on dots and nuke once he has aggro, you won't have much trouble.

Your main problem will be fights that require alot of moving around, but I think that'll be the same regardless of your class choice...

When you say £1800 - £2000, are you going with 5 new PCs? Would be interested to see which hardware you're planning to use, I'm having trouble finding a decent PC for under £600, but then again that's a rig capable of playing much newer games, and future games. Are you getting XKeys and KVM's etc with the setup? Currently I'm using 3 PCs hooked via KeyClone which works great, but 2 of the PCs are utter crap and I find it hard on the eyes and difficult to play for too long