Hi Rosaline,
Creating such an application definitively is possible, but ambitious if you are just starting with Mendix.
You could look online and on the forum (here for instance) on best practices for creating multi-tenant applications.
On the tenant you can store what rights they have to what ‘module’, and based on this model out the functionality, which is fairly simple. Show/don’t show buttons, add checks in microflows to show either a page with paid functionality, or a popup that says “this is paid-only content”, all this information can be retrieved at any time to validate with.
Good luck!