Selling Prototypes To Clients & The FCC
You state: "I would have to have it FCC tested before I could sell it." so I will take that as fact.

Then you go on to say "wanting to cash flow this project and being able to sell prototype devices" which seems like you want to circumvent the FCC rules in some way.

The biggest issue is trying to charge for your prototype. Of course people and companies build and test prototypes all the time. Further there is no problem demonstrating them to 3 parties etc. If your product will radiate RF energy that could potentially interfere with other devices then the responsible way to develop and test it is inside of a Faraday cage (basically a room with copper sheets on all surfaces that prevents RF from passing in or out. You could even loan it to a 3rd party for them to test inside their own Faraday cage.

Where you are going to get into big trouble (and face severe monetary and criminal penalties) is if you operate an unlicensed device that causes harmful interference to licensed operators, weather intentional or not. For example suppose because of a "bug" in your prototype it inadvertently radiated on a frequency used by aircraft and caused a 747 to crash....

Further this is something probably not covered by your insurance since it is most likely an illegal activity. . .

Bottom line - re-think your plan.