* you didn't specify anything the app *should* do besides "CRUD". You'll get better answers if you can say more about your needs and goals.
* some of the given requirements are mutually contradictory - "no services / SaaS" and "doesn't require a lot of maintenance", for instance. Part of the tradeoff you make using third-party services is "risk of them disappearing" vs "maintenance effort reduction".
* you didn't specify anything the app *should* do besides "CRUD". You'll get better answers if you can say more about your needs and goals.
* some of the given requirements are mutually contradictory - "no services / SaaS" and "doesn't require a lot of maintenance", for instance. Part of the tradeoff you make using third-party services is "risk of them disappearing" vs "maintenance effort reduction".