Building a Four Star as your first build is a great idea! I just finished my second (highly modified). As for size, that's a bit tougher of a decission. I went with the .40 so I could reuse the engine from my ARF trainer. This might be a good way to go. Even if you progress into warbirds and eventually larger birds, I'm sure you'll have no problem for finding a home for a good 40-50 size engine.
I have to say. The Four Star is a great plane and a good first build, but even then, it's best as a second flying plane.
Here's a photo of my fisrt, and my current Four Star.


Scott