Sa Tools ang maitutulong ko lang na advise sayo is either use
Android Studio(Java/Kotlin)
Flutter(Dart)
Choose the best for your current skills. The question is anong klase bang app ang idedevelop nyo? offline walang problema jan pero ano bang app yan. However, these are the things you need to have when developing Android App.:
A. Machine with atleast 4gb RAM.
B. Internet(Need when setting up AStudio if you opt to use it. Flutter, I dont know how to setup yet kasi di pa ako nagdevelop using it). I know you can configure it to work offline.
C. Java or Kotlin or Dart Knowledge
D. You should have at least knowledge about the basic Android app Components; Activities, Broadcast Receivers, Services, Content Providers(This is only required when your app needs to save sqlite data)
E. Ample time in development.