I think it allready was mentioned that you only can play humans. Perhaps the option to play gorrilas will be added some time in the future.
And the option to be neutral will not be in there. It was mentioned on IGN
http://pc.ign.com/articles/891/891471p1.htmlA lot of the story depends on that and your quests will be based on wether you are a hero or a villian.
Regarding single play missions I hope so as well. As far as I understood many quests will be scaled to your level and group size.