I'd lean towards the first two personally. Although I can understand that going with a large instance goes against the spirit of federated sites, there's plenty of work that goes into maintaining an instance, without even getting into the building & moderation of individual communities.
IMO, I think it'd be more beneficial to focus on problems around building a community, rather than solving the problems of maintaining a new instance on top of the former.
Fuckin love Infected Mushroom