I have two semi-serious PvE teams:

Team one:
Pally tank, played by somebody else.
Holy priest, played by somebody else.
Warlock, played by me.
2 x mages, played by me.

This is great fun, ticks all the boxes, and has been hugely successful so far. This is the one I look forward to playing the most, but which sadly gets neglected the most because of the need to co-ordinate with my wife and a good RL friend.

Team two (all played by me):
Pally tank, played using an X-stick.
Holy Priest, played using an X-keys pro and track ball.
Elemental Shammy
Frost Mage
Destro Warlock

Finding synergies between them was difficult, but that's actually the part I enjoy most about multi-boxing, and I solved that. The team's good, and so long as the Pally manages to hold aggro with his three button sequences, everything works really well.

Best of all, when they finaly ding 70 (80?! *shudder*...), I have five perfectly good characters to play solo in instances!

I'd never consider using that group in PvP though (which is far too dynamic for me to respond quickly with three different input devices), but it's great on my home PvE realm.

Not relaxing, but fun.

The disconnect issue doesn't seem to have a single solution that applies to everybody. I've recently moved onto running my five instances on three machines to and noticed two things that never used to happen before:

1. One of the characters - always the same one - gets disconnected periodically.

2. My "main" character. Lags like crazy at times, but in a very odd way. If I look at the other screens, I can see that he's still moving around the game world (which implies that he's transmitting), but nothing's being updated on his screen.

Under those conditions, I literally play by one of the other screens and after a delay (often many seconds - 5+ in most cases) it all updates.

I only use follow between encounters, and always break follow before an engagement. There's anecdotal evidence to suggest that this helps alot.

The "main character" problem I'm beginning to suspect is a client-side or machine issue. I've ordered a replacement network card (because I noted that even my browser stutters at the same time).

If I ever bottom this one out, I'll be sure to post about it!