JFBConnect, Joomla, Jomsocial and K2 intergratin

Yes, you shouldn't have any issues with your configuration above. JFBConnect has separate social profile plugins for Joomla (the User Profile plugin, if you use it), JomSocial and K2 and they can all be enabled at the same time. With that, when a user registers, you'll be able to import profile data into each of those extensions.

After they've registered, the users are treated like 100% standard Joomla users and you can modify their permissions however you want. When they return, they'll be logged in to the same Joomla account that was originally created for them with whatever permissions you may have modified.

I hope that helps explain, but if you have any other questions, just let me know.

Thanks,
Alex