Seems like the app is quite simple and should not grow too much in scope. You are lucky, it seems like a case where hybrid apps are interesting. There seems

Seems like the app is quite simple and should not grow too much in scope. You are lucky, it seems like a case where hybrid apps are interesting. There seems to exist an inflexion point where hybrid frameworks become an hindrance and it is more productive to just go with native. You should start by having a look at either Xamarin, Flutter or React Native. They are rather good multi platforms solutions.