Is there a modification available for 3.5 that restricts members on posting from certain sections of the forum until they have done a minimum number of posts? Also looking for one whereby nothing can be added to their signature unless they have done a minimum number.
The easiest way is via usergroup permissions and promotions.
ie, set the default registered users group (usergroupid=2) to have no permissions for signatures and to post only in the forums that you want them to post in, then set up a new usergroup with permissions for sigs and posting in all forums (except staff ones and any others you still don't want them to post in) then set up a promotion after x posts from the first usergroup to the second one.