From your onboarding list, it looks like you are hoping to override the Discourse trust level system. I think a better approach would be to use Discourse group membership to control access to your site’s content. For details about how this works, see Understanding groups and category permissions.
The WP Discourse plugin has a couple of functions that you can use to add and remove users from groups. Details are in this topic: Manage group membership in Discourse with WP Discourse SSO. That topic uses the PaidMembershipsPro plugin as an example, but the same idea should work with MemberPress.
Another topic that may have useful information is How to prevent some WP users from being able to login to Discourse.