Hi Daithi,
Cool thread! I'll be looking forward to hearing about your progress, and ultimately, of course, your immense success!
I have a similar project underway for an "educational" app, although, to be honest, I haven't gotten very far on my project. I don't expect to make buckets of money, but it would be nice to break even on the new MacBook that I'll need so that I can also port my apps to iOS.
I might be telling you something you already know; if so please pardon me. You have a couple of other choices other than writing a native Java app. You didn't say what kind of development environment you live in. If it happens to be .NET, you might be interested in
Mono for Android. The other development environment that sounds kind of interesting to me (again, I'm eventually planning to port my app to other OS'es) is
PhoneGap, which is an HTML5/Javascript environment.
Best of luck in your endeavor!