I tend to agree with GoldenEaglePilot - start in the uncertified (permit / homebuilt / microlight / experimental) market first of all to learn most of the lessons about the market and operating environment. Once established, start exploring whether there's a market in the certified world for any of your products, and at that point start thinking about what approvals you need for that specific equipment.
This is the route that has been taken by most of the newer companies in GA:whether it's avionics, engines, propellers, or whole aeroplanes over the last 30odd years, and it works.
G