I would add a few rules:

1. Don't accept people with negative trust. Could go with a rule like

Getting negative trust from DT2+ or spamming will cause you to be removed without payment.

2. Don't count posts in certain sections. Do you really want to pay people for claiming a giveaway in the Games and Rounds section, or post the same "It's a ponzi, don't invest" in the Investor Based Games section?

3. Don't count posts in 'spam megathreads', being threads that ask a simple question, and are thousands of posts long. No one reads them or really uses them, except for spammers to easily boost their post count. Some examples:

why some people don't believe in bitcoin? (4648 replies)
What are your plans with your Bitcoin?

I'd consider taking a look at other campaigns and seeing what rules they have. Best of luck with your campaign!