5 has always been my favorite number personally. It allows for a lot more interesting dynamics, players can break off into small groups to have more intimate conversations without leaving one person alone. Also from the standard Tank+Dps+Caster+healer it allows there to be a wildcard as well.

I’ve ran many games with 6 people, several with 8. It’s definitely doable, and you need to find a way to involve everyone. It helps if you take the ‘you do that thing’ mentality, which is where don’t fight them too too hard of they want to do something, like adding a lot of checks and such to show them down. Keep it flowing, and you’ll need to use the ‘well what do you think player-who-is-quiet’.