A couple things we need to get out of the way:

Should we have it be PVP?
Should we have neutral mobs? (Cows, sheep, etc.)
Should we have aggressive mobs? (Zombies, skeletons, etc.)

I'll give you more, once I have a list of what all we can change.

I, personally, am a fan of no PVP, or any mobs.

PVP, but only in arenas. I think all mobs should be on except for creepers.

Limited PVP, at most. Neutral mobs in small scales, aggresive mobs in even smaller scale, but existing.

Possibly only aggressive mobs in arenas because I saw servers where there were giant arenas with people putting all their stuff in chests and putting on diamond everything and seeing how many zombies they could kill, for example.