Most things have been covered-- the only other advice I might give:
Unless you have a LOT of free time, be sure you have the toons you want to take in to t6 figured out before doing t5. It is very likely you will not want to do another 5.0 quest from scratch for a different toon anytime soon after finishing t5 for the first time. Pick your core 6 wisely.
This exactly what I've been debating about. A lot of free time is something I don't have the luxury of, so I totally want to lock in on a core and only build out a second team after I've got them pretty rock solid. Bums me out to bail on my pet classes, but so be it.