Need advice for setting up my first deployable project

I am a computer science student who works part time at a fast food restaurant. In the few years I’ve been working there I’ve noticed a lot of problems that could be solved by introducing new software. I have confidence in my ability to complete the project but I’m having a hard time finding a starting point. My goal is to create a mobile/web app that can handle a large user base (of both employees and management) and it also needs to be scalable for the future. I would like to use flutter but I’m not sure is that’s the right choice. Any feedback is appreciated, thanks.

TLDR: Looking to make and sell software to businesses for the first time and I need advice.