Meh. It's a great phone. I'm happy with it.
If you want almost guaranteed cross platform portability, then why not implement your system as a website? Particularly if all the app does is...
I said it doesn't sound great for the reasons you yourself gave - that it's unmaintained, and there's no documentation!
I have no experience if...
We have a procedure for developers to announce their apps. Read this thread for instructions.
Developer Announcement Procedure
Doesn't sound like a great thing to be using. Any particular reason why you want to use it?
You could also consider using Apache Cordova.
Some suggestions here:
A gradle sync is worth trying
File -> Sync Project...
Oh no! Not good news. Best wishes for a speedy recovery.