Default user roles in multisite

Hello:

I have only just realized that new users are being assigned a role of “Participant” when they create user accounts on my network. As a result, they are not able to even log into their own profile pages. At least, I was not able to do this on a test user account. I kept receiving the error “You do not have sufficient permissions to access this page.” I changed the role of this user to “Subscriber” and was then able to access that user’s profile page when logging in as him.

“Participant” is a role assigned by the bbPress plugin, and it seems to give it by default to all users. I want users to be assigned a site role of Subscriber automatically, or else it is not possible for them to do anything other than visit the main page and the forums. But it seems there is no New User Default Role setting like there is on single site setups. Is there a recommended workaround here?

And, a third question: How do users who initially sign up and only create a user account, but no website, later add a site to that user account? I am not seeing any way for them to do this, whether they are logged in as Participant or Subscriber. If they only create a user account at first, is it not possible for them to create a site later?