Re: Can Groups, Blogs, Members home page use Member Theme?
I recommend copying all of the contents of BuddyPress Home to a new directory, modifying the style.css to a new name, comparing your existing WP header.php/footer.php files to the ones in your new directory, taking out all the WordPress specific PHP function references and replacing them WordPress MU/BuddyPress ones. Tedious, but effective.
I found that the main hurdle when doing this kind of migration (for me) was letting go of my old WordPress ways of doing things. I.E. no longer using the page widget as my main navigation menu, etc… Which you can still do if you want to, there’s nothing stopping you. The functions are still the same, but you’ll still want to use the BuddyPress home theme as your starting point, as it gives you the building blocks towards integrating your existing theme with the new platform.