Is there a cap on the difficulty increase for the payout?
Yes, any difficulty increase above 100 million will pay maximum 0.01 BTC/share and no more.
If I purchase the future at .009 and it settles at .008 - the .001 represents the COST to me to protect my investment, right?
If I purchase the future at .009 and it settles at .01 - the .001 represents protection benefit of the hedge, do I have that correct?
If so, then assume I've purchase 500 Gh/s of mining equipment I wish to hedge. How many futures should I purchase?
First two questions - yes, correct.
The last question cannot be answered without more precise formulation what is exactly your goal. If your goal is to keep the profit fully at 0.20 BTC per GH/s in next 6 months even if difficulty increases by 30% every time or more (as per your table), you need the future to earn you 0.2 * 500 = 100 BTC. You can earn this from the difference between current sell price ~ 0.008 and maximum 0.01 per share = 0.002 . This means you need 100/0.002 = 50000 shares of CB.IDIFF-O... but sadly, there isn't such a depth. Maybe in future when it will get established and backed by bigger investor than us.
Also, you can wait for introduction of CB.IDIFF-E October in ~ 2 weeks, which might better suit you time-wise.