Domain mapping and multi-networking

Hi All,
It seems I'm in the the group building a national association.
They want to set up a directory and do multisite testing with BuddyPress there. It won't be the final domain the final/main domain will be moved to the network later. They will be separate domains but on the same network.
I've used mutil-site, multi-network and even multi-BuddyPress. Does anyone know if multi-network and multi-BuddyPress can be run together? Is there a better way to build a national network with thousands of members having different categories with many groups in each category.

Oh by the way, they are charging annual membersips.

Remember, simple is better.

Thanks for your time
Richard