Supabase was a great discovery: affordable, easy, fast, and robust. It is the best alternative to Firebase.
Figma is Figma. It's the easiest tool for creating your layouts, and what really surprises me every time is how fluid it is in big projects with many screens.
I used FlutterFlow to develop the app, utilizing basically all functions. The main advantage is that the code is yours; you will never be locked in. Additionally, they update the app every month.