How best to set up Multisite Buddypress?

Hi guys is set up as a multi-site with Domain Mapping , intended to facilitate local travel portals as part of one network, eg EnjoyScotland.Travel,
I want to implement Buddypress, for main features like uploading and share photo albums ('My Edinburgh vacation etc.), friending, etc.
I also want to use Group Events plugin so members can start a BP group for a festival for example, and they can then post multiple small events that make it up.
I've installed Buddypress, so now I'm wondering how to install & configure. For example should I activate it network-wide, or by site? How do I configure the Registration pages on the local sub-sites etc?

Any guidance appreciated,
cheers, Neil.