I'll end up making mine kind of realistic to what we currently have.
Even then though, going down from a 25 man we have usually around 32 active to keep a full roster going. I would say slim that down to 25 to keep a full roster going on 20 man.
5 heals (just as Blizz said it would need it but people would have OS to either increase or decrease this)
13 dps, with even split with slight favor to ranged of 6 melee 7 ranged
Our GM/RL is a ret pally so 5 slots besides that http://raidcomp.mmo-champion.com/?c=...00000000000000