I say focus on the structure of the "program", then take specific votes on the details. Do you want levels of members to roughly correspond with Y-Combinator's classes/timeline? The statuses could be: Applied (need social validation to get it), Level 1 (approximately 1 month into Y-Com), Level 2 (mo 2), Level 3, Alumni.

I definitely say use off the shelf software wherever possible. I also think there needs to be some kind of "voting off the island" type situation. Maybe of a given group that starts, only x-percentage can finish. Part of Y-combinator's appeal is that it selects positively for good companies. If it is completely open, you will loose some of this.

I agree that you will need some kind of identification walls in order to make people comfortable working within it, and to make it special. My company, signnow, has a product notarynow that I would gladly donate our service to solidly identify people, if you like.