Some questions (from a Social Engine user)
Design and Skin Customization
JR can do anything SE can pretty much, so that's not a problem. Jamroom can easily make "community" type pages, etc, listing anything from your profiles any way you want.
If you plan on having a small niche site, that's all good. I would
highly recommend that if you plan on having a lot of users online at the same time interacting with your site, you avoid "community" style pages. Imagine that page you posted a screenshot of with 500 people posting at the same time - it would be unusable. This is why when you go to facebook or twitter there is no "community" section - all the interaction takes place on your profile or other users profiles.
Of course it's 100% up to you, but having been doing this for a very long time I've seen many sites really struggle with performance as many of the features that work great on a small, intimate site suddenly blow up once they get a surge in users.