WPMU Existing plugin customization

We have WordPress MU Membership plugin for our Multi-Site project. Plugin link:- [login to view URL] We want to modify it little bit as per our requirements. Requirement 1. Add pages and posts limit, plugin access limit, theme access limit on subscription plan creating form from the admin section of WP MU. (general page, post, plugin and theme access limitations are available on supporter plugin, you can use it for fast work, we need advanced as per our requirement) for example:- Silver Subscribers have only 2 pages and 20 posts create facility, some basic plugins and some simple theme access facility. Gold Subscribers have only 6 pages and 60 posts create facility, some advanced plugins and some spceail CMS like theme access facility. Diamond Subscribers have 15 pages(or unlimited) and 150 posts create facility, All plugins and all themes access facility. Requirement 2. Update / Integrate our payment gateway... DirecPay, see its detail at [login to view URL] AND/OR [login to view URL]