Adding my 2 cents...

I would transfer all of the unique high level toons from my 3-5th accounts back to my first two accounts. I've got too many toons to fit them all on my main account now, but I'd salavage: my 80 priest, 80 hunter, 2 of my 72 paladins, 2 of my 60 shamen, my 60 druid, my 60 lock, my 60 rogue and 2 of my death knights. That'd have to be enough. My guild is getting back into raiding. I really enjoy casual raiding, so I'd stick around and play solo.

I wouldn't multibox anymore, except for the greatest multiboxing oppertunity in the game:

The Auction Houses! (I've got two lowbie alliance on my main acct and another on my 2nd acct to help find goods for guildes when the horde auction is overpriced or doesn't have the goods). It's also nice to have one of your bank toons on and shopping while you're doing other things on the other account with a high level toon.