Initial Thoughts

I've been kicking around with some ideas for the first project to really get stuck into.  I'm pretty happy with my decision, but I'm not going to give too much away just yet as I dont want anybody to steal my idea! 
But where to start on such a project. 

This app will be huge.  But I need to make sure that the files size is not too big to put people off from downloading it.  The last thing I want to do is spend time and effort producing an app only to find that nobody downloads it at all.

There a few technical issues that I need to find out about, and make sure that I am able to produce the code to make it work.  I've got the knowledge to be able to design an app to a certain level, but I'm sure I will need to learn more to produce the best Android Apps that I can.