I would go with Web2Py over Django as it is faster to learn and will allow you to rapidly prototype a back-end and database schema in SQL Lite. If you need to run both a local database and back-end database, web2py will build the SQL Lite database for you to copy to your AppStudio/local database. Restful services are automatically done for you as you build CRUD forms and building dedicated Restful services is well documented.
Web2Py is about to have a sister technology, Web3Py, which leverage the lessons from Web2Py and builds dedicated restful services that operate 10X faster but you implement the front end using AppStudio, Vue or some other front end.
Web2Py is plenty scalable as I have written apps handling 1000s of concurrent users and the guidelines for app optimization are very easy and straitforward.