You want to build something that people find and continuously use. So even if you only get 5 new users a day, after a few years you have many thousands of users

You want to build something that people find and continuously use. So even if you only get 5 new users a day, after a few years you have many thousands of users. What do people continuously use over years? Think tools, things that improve their productivity, things that help them. Monetization is pretty easy, as mobile ads pay well, and you can charge an SaaS subscription to remove ads, or consumables to get extra features. A free install is critical or no one will use it, charge on upsells within a free app. This is an inexact science. This is inherently a risky endeavor, with a high probability of failure. You need to be mentally prepared to fail. Good luck