BuddyPress.org

I never used Buddypress.
I’m working at a wordpress project that is structured as follows in a multisite configuration:

1) main site, single language, heavily customized with post types, loads of content, no forum, one webshop
2) secondary site, simpler setup, relatively little content, no forum, no webshop, multilanguage (WPML)
3) third site hosting a forum only and no other content; forum interface will be multilanguage (like site #2)
4) fourth site, reserved to admins only, single language, possibly a forum, to manage content and carry on project management tasks and discussions, etc.

– all sites would be in the same domain (ie http://www.domain.com/ = 1, http://www.domain.com/2, http://www.domain.com/3 etc)

– sites #1, #2, #3 would be seamlessly integrated in the frontend. However content displayed changes, since #1 has very different contents meant for users in the main language, while #3 is just a forum. Site #2 is intended to provide information and basic contents to international users, while the forum would provide a common space for discussion, being the interface translated.

I want a multisite setup so users can keep their logins, cookies, across the sites, yet at the same time make some order to admin the different areas.

Now… it is clear to me that WPML I can take care of the translation part. However, what I’m really clueless about is how to seamlessly integrate the forum part. Since mine is a community-type website, I want to have community features… Buddypress seems to offer a more complete solution for this than bare bbpress. I don’t want users to create their blogs or groups. But it would be nice to have better profile pages, private messaging, set their own display pic, and so on. Features that bbpress lacks or are not natively integrated (I come from a bbpress 1.0 experience and while I love it for the theming possibilities, plugin wise was badly supported).

So what I would really like to know… Does it make sense to run BuddyPress on site #3, activate only modules for member profiles, forums and activity streams?

Will the activity streams report activity of these users on sites #1 and #2? (would that include creation of new articles, posts and content by admins and authors? or just comments?)

Will the users be able to login from site #1 or #2 or #3 and kept logged in without any weirdness happening when navigating through the sites and performing actions?

Can authors from #1 and #2 link their profiles to profiles found in #3 Buddypress rather than using author.php? Same for registered users that post a comment on #1 or #2, can they have a link directing to their Buddypress member profile page/activity stream?

Being site #1 only in one language for both content and interface, what if user jumps from #2 or #3 to #1 and then back to #2 or #3, would his languages preference being persistent?

Thank you!