There's an aft overlook on deck 7 and deck 8; the one on deck 7 is significantly bigger. Not a lot of chairs on either deck, but you could host a pretty big meeting back there on Deck 7 if people didn't mind standing. (They call it a "secret deck", but I'm not sure why -- there's a big sign on the door that says "Aft Overlook: Doors locked from 11:00 p.m. to 7:00 a.m." Maybe it's called "secret" because not a lot of people would necessarily wander back there on those two decks, unless you had an aft stateroom there.)
All that being said, from what I saw, the promenade lounge on Deck 3 was practically deserted for most of the 5/8 Wonder cruise, and I'm guessing you'd be a lot more comfortable meeting there, or maybe up on Deck 10 overlooking the pools.