How do I set up specific responses for different levels of membership

Hi guys,

First off, thanx for the gr8 plugins and support! My setup is WP 3.5.1, BP 1.7.

Secondly, I have come up against a bit of a stumbling block and need help.
Trying to setup a membership site where there are 3 levels of access. Visitor, registered and premium.
Visitors is pretty self explanatory, registered is just a user that can view and send friend requests but cannot send private messages and premium is paid for membership which unlocks all the doors (pretty much)
I need the "Membership" plugin to allow premium members to send messages to registered users but not the other way around and of course for the registered user to have to "upgrade" in order to view the message from the premium member. That's the first question, the second one being how to create the path so when the registered user gets the message from the premium member, they can click a button to upgrade their membership.

Hope that's possible.

Thanx,

D.