Need plugin advice for specific funtionality

Could someone point me in the right direction finding 1 or more than 1 plugins that would do the following:

I’ll use John as the example user.

John comes to the site and registers
John creates a list of questions/topics.
John invites a select group of other people to comment on the questions/topics.
Only John and his invitees may see John’s questions/topics.
Other users may create their own question/topic “area”.

Any advice would be appreciated.