Art of the possible with Multisite and Buddypress

I'm at a junction as to whether Multisite with Buddypress can actually do what I thought it could do and would appreciate some advice:

I’m looking to configure ….

Members of a top level site to be able to create member blogs, where these blogs serve a sub-community with similar Buddypress features to that of the top level site.

Importantly content posted and membership information is aggregated up to the top level site from the member blog but at this member blog level members who register (or join via an invitation) are the only ones listed as members (ie. NOT the member list of the wider community).

Also I really wanted the ability to allow all member blogs to manage their own Buddypress groups that are visible and managed at this member blog level (not the potential for an unorganised mass of groups at the top level site).

Note. However members should not be allowed to create sub blogs themselves from their own site (just 2 levels of blogs and then a group level).

In Summary a hierarchy that serves similar functions only to members at that level:

Main Site Member Blog Buddypress Group
-------------- ------------------------ ---------------------------
Main Community –> sub communityA –> groupA1
–> groupA2
–> etc…

–> sub communityB –> groupB1
–> groupB2
–> etc…
–> etc…
<————————Content aggregation and membership visibility

Can I do this or am I banging my head against a brick wall for good reason?

If it can be done how would one set-up Buddypress particularly and how is registration and visibility of members managed on sub blogs?

If this isnt possible can I get close to this set-up by various means?