The playable races should depend on the story. Some races may not make sense then. I don't know how an Imp would fit into it for example. If the trailer has a meaning and the uncommon concord of the races shown (Orcs were only enemies in earlier Divinity titles) does play a role in the story, all these races should be playable. Personally I need one playable race, Humans (although in DOS 2 I played as an Elf), but others might have much higher expectations.
It may be an unpopular sight, but I prefer a group of 4. It is more difficult to balance combat with bigger groups and it is for me, as single-player-only player, of course easier to learn and play 4 classes/roles than 5 or 6. In BG 3 I was not able despite several trials to get a satisfying gameplay with more than 4 chars in the party. It always felt too difficult or (mostly) too easy. In the end I played with 4 with the difficulty mods installed to justify 5 party members.
