All the things are sucks let me explain why?
Ionic use html, css, javascript when you go in depth its become complex.
React nativ will help you to handle ui using javascript.
Saas is cloud computing concept that make you adictive like facebook it just sell you small product in in cloud platform.
when you know little python and java you build android apps and you build django apps its work like a brize.
Retrofit use grab data using http request that mixes all over.
Livedata will help you for live syncronizacation.
Room use on top of sql light.
Dagger use for scincronizacating data.
Rxjava is a data mass.
Its much more simpler, model view controllar read update delet add all are important concept.
So the solution is very simple use android studio to build averything learn things deeply what all the servicess can do you can do using java as a programming language, android studio as a platform , SQL light as a database.
Biswas 