[ED4] How to create private forums?

Hello,

I'd like to know if there is a way to create private forums for members,
I mean one forum by member, that he would be the only one to see and to use with the staff team?

Is the solution to create one Joomla group by member and to give permissions to these groups one by one?
If yes, knowing there will have about 100 members, could it be a problem to have so many Joomla groups?

Thanks