There's a lot to learn and its easy to fall down a few different rabbit holes. What I recommend is starting with a simple app that mimics the core 80% of functionality found in most apps and then expanding from there. This way you get to learn as you go but all the while have the basis for something that can actually be deployed (vs feeling just like a toy to start all over again from.)
We're going to build an app that will enable people to find or become remote coaches to others. This is a classic two-sided market app, where the value is in connecting two people together based on specific criteria.