Planet13 - 8:37 pm on Dec 7, 2011 (gmt 0)
I can't say anything about any of the formats, but...
If you are going to have 30 sites, I think the thing you are going to need most is GREAT CONTENT, so I think you are probably going to have to spend most of your time finding people who can contribute to your blogs.
i don't know how much page rank will flow from those sites to your main site if those 30 sites don't have lot of naturally acquired links pointing to them, and the best way to get natural links is through great content and letting people know that you have great content.
I hope this helps.