Chat

For now I think the most important thing is simply keeping discussion in the big / obvious / front-page areas active enough that new users see that it's a lively community. We don't necessarily have to recreate every esoteric subreddit right away, that can come in time; the important thing is that whenever a new person shows up they see a bunch of recent posts and a bunch of recent comments (and not a ton of spam / ads / whatever).

Think of it a bit like walking around a city you don't know and trying to pick out a restaurant to have dinner at - maybe you can't find your favorite cuisine, but if a place looks clean and new and lively and the bar is well-stocked then perhaps it's OK if the menu is a bunch of New American blah blah whatever because you're still going to end up happy and fed. (and can note with interest the sign about the Romanian Enchilada place that's opening next month and remind yourself to come back then)