How to set up user funtions properly?

Issue Summary

Dear all,

thank you for providing this module at all. I installed it on my multisite and it works as expected. Now I would like to expand my websites with more modules and features.

Unfortunately I do have a problem with the handling of user related information:

The main site www.example.com offers the opportunity to register and users can then set bookmarks and comment on content. So far so good.
The first sub-website sub1.example.com is the community website for the main website offering forums, blogs, etc. It should also provide social media features as twitter, facebook, etc. and the profiles should be expanded by more fields.
The second sub-website sub2.example.com provides an store system with Amazon Store and Drupal Commerce.

Now, please explain to me how to handle this. Do the registered users need to handle all the community user related stuff on the main website? Or can I just activate the modules on sub1 and sub2 and have them adjust their settings on those sites?

In the documentation it only says that the log-in needs to be on example.com. It tells nothing about where to care for the account and community issues.

Please help me out on this one. Thank you!

Kirsten