I'm trying a couple 5-man teams to see what I like, and so far the 1xPaladin/4xShaman setup seems to be the easiest to control. Using more classes, like 5, takes a lot of micro-managing, and is not as efficient since you're going to miss spell/shot rotations more frequently. If you want flexibility for end-game guild choices, go ahead and play multiple classes (only 1 melee at a time). I really wouldn't bother with more than 3 classes if you're going to try end-game instances on your own though.

It's easier to start by playing 5 different classes and just get used to playing that style than to start with 1 or 2 classes, getting used to that, then attempting 5 classes. It's been difficult to go back to my 5-class team after my 2-class (paladin/shaman) team for awhile.