I think running a tank,healer and 3 of the same dps will be the most simple way to go, just like WoW. But more so in Rift due to less macro flexibility. I'm going to be trying multi-bards. They do a ton of passive healing. I think you could get away with 5 bards for anything in the open world, and maybe duel spec one as a tank for dungons. I talk about that in my thread on bards. http://www.dual-boxing.com/showthread.php?t=34540

But its too early to know for sure. if you want instance viability, i would say tank..healer and 3 high ranged dps would be best bet. There are SOOO many combinations of classes and souls atm. i think thats a good thing, it will be fun trying to figure it all out!