First, I really appreciate the time everyone has taken to help me understand this. THANK YOU.
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.
I think I finally get it. Using my OP table....
Assume I believe I will receive the units on October 1 & the difficulty will increase 25%.
Then, if I wish to hedge against an increase to 30% (reducing profit by .08 / Gh)....
I need to purchase .08 / .002 = 40 future contracts per Gh /s of purchased mining equipment.
Hedging against a future delivery date (say November 1 rather than October 1) I need to purchase (.11 / .002) = 55 future contracts per Gh/s of purchased mining equipment.
I suppose the final point is the cost of those contracts.... represented in either a) growth below 25%; or b) arrival of equipment before October 1. Therefore, I just need to compare the cost of the hedge to determine how to proceed.