Membership plugin

I have 2 issues on my site I want a plugin to help. First we aren’t using any sort of plugin for member/user information, all seems to be managed by users section. We have a quiz that is free to registered users/paid members but the only way it will differentiate is if the paid members say they have a pin number and add it into the form when registering for the test. But that pin number is just a generic field, you could put in any 6 digit number and get free access as a member. I want the free access to the quiz to be restricted to members. I also want it to send auto emails to members prior to expiration. Thats all I need it to do, those 2 things. A lot of the membership plugins seem like overkill. Any recommendations?