Probably an important factor to consider is.......pick a scale model that you really like. In other words if a P-51 is the most "beautiful" plane to you then you would most likely stick with the project to the end. Your enthusiasm should stay high and you would be willing to spend more, add more details, improve your flying skills more, etc, just to maximize the experience.

But if you pick a subject that is just OK you might loose momentum and quit. I have on some of mine and realized that they were an impuse purchase at the time, etc.

Also a kit that has a lot of scale fidelity right off of the shelf might help speed things along.
My 2cents.