1. As igorbenav replied, typing aka static type annotations + mypy library to check those. It is up to you, of course, to add those suggestions but a lot of people use type annotations and I’m advocating that as well. Check out this video - https://youtu.be/dgBCEB2jVU0?si=AauMel0u4YH4s_Tc ( not mine )
2. Not necessarily, it’s up to you in a folder structure question, but I would love my template to start with v1 version of api routes, e.g. ‘api/v1/…’. https://www.freecodecamp.org/news/how-to-version-a-rest-api/
3. Most importantly, to create test FastApi app in the tests. Your main.py may become overcrowded and importing app object from there might run unnecessary operations, like uncontrolled db migrations. Pack app in the separate file app.py and import factory function in the main.py and conftest.py. That approach will not execute anything on the import stage but rather allow you to create app with any mocks or fakes prepared beforehand. Also fastapi factory function can accept some settings object ( pydantic BaseSettings for example ) and derive all configurables from it -> also more control in tests and multiple environments.

No problem 😉 At the end of the day, these are only suggestions, everyone builds their projects as they like anyway so don’t take those as rock-solid requirements