I have a home-based business that I work at a few hours (if that) a MONTH. I have had that even during my application phase (and SSA knows this). I think (and I may be wrong) the biggest thing is that you're not working FULL TIME and trying to get disability. Its hard to prove you can't work full time if you're working full time.
I realize wanting disability so you don't go downhill with your disease is a very valid and real point for CFers... I applied back in 1999 and after 2 years of fighting (and actually I even MET one of the criteria), they denied me at the federal level. One of the points made at some point was that in order to stay healthy I couldn't work. That is NOT what you want to go on. SSA doesn't care if you're going to get sick or rundown cause you work. Its for people who literally CANNOT work full time because they're already too sick.
Its a tough system and exceedingly frustrating, but you could certainly apply and see what comes of if. However, having CF alone does not garuantee you benefits. There are criteria and proof you have to show before they'll give you disability. Please check out my link above. If you don't fit the criteria for cystic fibrosis, you likely will have a "fight" on your hands. Not sure how many people win when they don't fit into the criteria, but even when I DID fit into the criteria back in 1999, I was denied all the way to the federal level. So, its daunting to say the least. There are a lot of factors that come into play such as representation when you appeal, a knowledgable physician examining your case, correct and consise medical documents, etc.
Good luck to you whatever you decide to do!