I used VueJS with the Vuetify material-design UI framework. Half of my goal with this project was just to learn something new, and so far working with Vue and Vuetify has been fantastic.
Yes, the data files were from the APK itself. The game runs on Unity engine, so any Unity asset tool will do the job once you unzip the APK. I do know that updated data files are grabbed off the internet to the game on launch, but have not been able to incorporate these yet.