An interesting way of making yourself some BTC OP.
If it works then I'll genuinely be impressed. It'd probably be one of the easiest ways of making 0.5BTC in today's market.
Having been said, getting 7500 members to participate in this would be near impossible. Even those that do join aren't even guaranteed to send you the BTC as they may think the odds of them winning are slim.
I'll give you credit for the idea but it's definitely not going to work. Maybe try with a smaller pool of players for a smaller prize and perhaps you may be on to something...

Edit: Just saw the update. Getting 300 members may be more realistic but setting the minimum at 300k satoshi isn't.