Buddypress / multisite design. Is pro sites my best choice?

Hi. I’m not sure where to begin, which tools to use to achieve my end goal.

I would like to build a community around a common shared interest / niche. I would like to offer a social community that people can join for free and have a simple blog for free using the same theme as the buddypress site. So far I can’t figure out how user blogs can use the same theme as bp site, they seem to get 2012 by default.

I would also like to offer a premium option or two that gives them an opportunity to host a more advanced site, including domain etc.

Additionally I would like to be able to design and host sites with custom designed themes and plugins. I would like these to also be a part of the community. There would be distinct user benefit there.

(if I use pro sites, can I override levels on a site to site basis?)

I would ideally like visitors who are not logged in to be presented only with several pages of my choice (presentation / call to action to join etc., kind of like fb does it I guess) until they join and log in, they won’t have full access to the content on the main buddypress site but of course if they go to a user site directly they will be able to read everything there.

I have several self owned existing WordPress single sites each with their own domains already. I would like these to be rolled in tithe community as well. When I create the community will they automatically becomes part of it? They are currently part of my multisite install.

That should keep us busy for awhile. Many thanks in advance.