Migrate current Wordpress membership plugin("s2member") to a new membership plugin

We require a very skilled and smart Wordpress Developer to help us with this project. We have a membership site utilizing a plugin called s2member as it's membership control. This plugin is crap and has caused us so many issues. We would like to move to a completely different membership plugin. Basically, all of our content on the site is tied into this plugin. Therefore, we would need an overhaul of this in order to make the site work just like its current state without affecting any users. Some requirements: 1. migrate entire website from using s2member plugin as the membership control to a different plugin(we need to decide this one). - includes pages, posts, some shortcode, payment capabilities 2. keep all functionality the same, but running under a new plugin 3. You must test everything in order to ensure a bug free application - unit test coverage 4. you need to come up with a defined plan of this migration. The steps required to make this happen and the impact on the users. We do have the option of a staging environment with our hosting service, so we could probably utilize that 5. make sure that users are able to go successfully through sign up, login, upgrade, cancellation functionality 6. Basically, as stated before, we are attempting to move from one membership platform to another. Leaving all functionality in tact and impacting no users. 7. Must work in an Agile fashion. You will have 1-2 week Sprints. After which some shippable component needs to be in place. We can discuss this further. More in depth requirements will follow post discussion.