Re: css broke my buddypress
The skeleton theme is a bare-bones HTML theme that exists for you to add your custom CSS to, so yes absolutely go nuts and edit until your heart’s content. 
I would suggest, however, that if you are new to BuddyPress, that you start off with the Release Candidate rather than 1.0. It will give you a head start on what is coming by the time you’re comfortable enough to go live.
