Where to even begin?

Hey all! Got referred here from r/entrepreneurRideAlong

I'm a junior ios engineer by trade and have recently thought about building a platform in the sharing economy space to facilitate either (undecided) the trading of watches or investment portfolios.

I am completely clueless on where to even start.

I've just been doing market research (or what I think is market research) by reading up on anything and everything I can about the history and the science and the forecasts of the sharing economy business model. Once I think I understand it more, I'll begin hitting any forums and online communities I can find and just start tossing out surveys to try and identify if there's even a demand for what I'm trying to build, and ask questions to try and gauge what sort of challenges and problems I'll need to solve.

I'm hesitant on actually starting to write any code (especially since I'm still quite new in my engineering career), as I've read it's better to validate the idea first before doing any serious work.

I've also been thinking about recruiting help from a couple of my friends who are entrepreneur-minded. I don't think there's any specific skillset they can offer but just thinking two heads are better than one.

Any insights or feedback highly appreciated!