You are competing against Amazon at that point, I would pick an underserved niche that you are most passionate / knowledgeable about and start there. For instance, drone after market accessories like stickers, lights, carrying cases, etc. Look for some trends using Google, Pinterest, etc. It's business 101, find a need and serve it. Your best bet is to focus and go very deep, than casting a wide net because you're resources will be spread to thinly. I'd be more than happy to help you narrow your list and am available any time for a call. Good luck!