BuddyPress.org

Hello guys, I have a question. First, a little bit of history.
I have WP latest version, multisite installed in root, sub-folders on a shared webhosting service. Buddypress is installed as a secondary blog (example.com/community), as I want the site theme style to be different from main site.
I use mutliste user management plugin

Aspiration
I would like new users to sign up to new sites via main site (example.com) and get the welcome email from example.com site.

I would like new users (eg subscribers) to log in from example.com site, only

Question
Shall I activate buddypress on second blog only, or network wide?

Thank you for your support.

Regards, strategizeme