Member site advice

I would like a membership site that allows people to sign up for regions they are interested in. My thought was to make each region a separate blog. Each region pretty much manages itself so this made this most sense. However, I would also like members to sign up for the network and be able to choose regions/blogs that they are interested in so we can send emails accordingly.

Is this the best way to go about this? Or is there a better way to make this happen?
I appreciate all input!