Set up MemberPress on a Wordpress based site

We have a WordPress based site with all-custom templates. The site is not a "normal" business site. It is intended to allow people to create posts and then view only their own posts. They use their posts as online visual aids. This is done through a custom post type and a custom template with specific CSS and scripts. We need to add MemberPress protection to this site, so that: a. All users may sign up for a free account and will be able to see a few posts; b. "Creator" users can make and view their own walls for a monthly charge; c. "Annual" subscribers can view certain posts for a year; d. "Semester" subscribers can view certain posts for a semester. We need: 1. A login link on the front page for existing subscribers; 2. A sign up link on the front page for new subscribers; 3. To make sure the subscriptions are set up correctly (there are tags on the various posts so the protection shouldn't be difficult). 4. Separate pages to subscribe to each subscription (the subscriptions are not related to one another so putting them all on one page doesn't make sense and is confusing to users). We will link separately to the subscription pages for each from the main menu. We have an active subscription for MemberPress. The templates for this site were done from scratch. They are very basic in some ways, but they do exactly -- and only -- what we need. We need to keep all the functionality in functions.php. If there are conflicts with MemberPress, it doesn't matter HOW the functionality is kept, but it has to be kept somehow.