My b2evolution Version: 2.x

Hi all,
I have a little problem with permissions.

I need a group of users who can leave comments without moderation.
I meant:

Visitors and basic registered users can leave comments in draft mode, admin approvation is required for publishing (and that's the default blog configuration).

Trusted users group can leave comments without admin approval, sent comments are automatically published.

No one except admin can make blog, see back-office stuff, stats, write posts or anything else.

How can I reach the goal?

Thanks in advance and sorry for my "raw" english.