Suggestions for the structure of a membership real estate site

I do a lot of work with themes for wordpress and I have a couple of spectacular niche domain names that I’ve been sitting on for years.

I want to build a membership site where the agents can sign up for an annual membership, have access to a private forum/mini social network where they can communicate, etc. Once they are members, they can add listings, though not as much detail will be necessary as a traditional site.

Anyway, what I’m getting at is that I’m trying to figure out the best way to run this, e.g. what plugins to use, whether to use buddypress or mu, what good membership plugins there are, any mapping plugins that can aggregate the listings, etc.

I’m pretty new to WPMUdev and I’m curious how others would approach this. I am pretty committed to using WP because I adore it and I’m very comfortable working with it, but I don’t have much experience with buddypress or mu.