If you're raiding...

Balance your group to provide close to an even distribution of tokens/armor types.
And ensure you have close to all buffs, including procs.
And close to all debuffs.
You would like the ability to cleanse/resist each type of Curse (Poison/Disease/Magic) effect too.

Range DPS, in general, seems easier than melee DPS.

And a heal system that works is probably going to be one of the most important considerations.

Dual-Spec is another consideration, as a DPS/Healer druid (in the place of one of your two tanks) will be much more beneficial than a second tank, in an encounter which requires only one tank.



I would take a look at some of Mercurio's posts, as he was successfully running three different 10-man raid compositions during the WotLK era.
Maybe he still is, or maybe not.

But that is still going to give a good insight as to what was needed then, which you can adapt for now.