Ticket system and Dashboard?

First off, make sure you're using PDO and prepare all your statements.
Second off you would basically do something like this
>insert in tickets "id(NULL)" "title", "username", "userid", "content"

And to reply to the ticket you would basically have a table called "messages", with this
"message", "username", "userid", "ticketID"

Where ticketID is the ticket's row id.

You can work with Slut's IPN for the membership and when they purchased update the users "membership" to 1 and it's 0 by default.

As for the admin dashboard, basically you can set the user's rank to 1, where 0 is registered and 1 is admin.
If user's rank == 1, display the admin sidebar. if not display the other sidebar.

Pm me your skype, ill help if necessary