Map, filter, and reduce your ideas. Health, fitness, and healthcare all fall into the same bucket. However, the money is in helping companies operate more efficiently. Lots of great opportunities in the area of automation. I would start talking to people who work in healthcare companies about how they process their data. They still rely heavily on copying and pasting from excel spreadsheets. To give you an idea, I just built a system to do such thing at work. Took me a 2 days. It could easily be replicated and sold as a sass or onetime purchase. Plus it is selking shovels because no one likes to process data manually.
Environment wise, I'd say that there is opportunity in the data collection side (this would make you a middleman). Lots of orgs need a way to CRUD localized enviromental data. Look into it.
About dividing and conquering.
Again: map, filter, and reduce. Map your ideas to business models (money making functions). Filter them to remove the ones who don't have a clear path to revenue. Reduce down to the one you can execute. Take your time.