Questions about buddypress

Hello,

We are triing to build a community for catalan blogs, our aim is to allow users to create their blogs, and share a community between them…

for that we decided to use buddypress, but have questions on how to configure it…

We want to have ONLY one community, not one for each blog, if I’m correct, this is usual buddypress+WPMU, and we think is working now…

We would like that users can customize the templates for their blog, but, as most are not configured for buddpress, they look horrible sometimes…

then, is it possible to have a default theme for buddypress that is same across all blogs, independently of the theme on that blog…

Regards