I don't see any mention of calculations around difficulty changes?
I did not incorporate the bitcoin difficulty change, the only way I believe this can be done is to update my business plan everytime the difficulty changes, which I monitor constantly.
That's probably a good idea. It might also be a good idea to set up some sort of SMS alert system so you don't get surprised if the difficulty changes while you're sleeping. How often do you think you'll need to update your business plan?