What I love about modeling is that there is no limit to what you can do. If you have the time, the money, and the motivation you can build as much or as little as you want. I mean, if you want a complete navy made out of matchsticks then go for it. If you want a mechanically functioning 1/16 scale aluminum P-51 or F-4U Corsair, or even a model made entirely out of leftovers, nothing should keep you from fulfilling your vision! Me? Well, my vision doesn't include me going crazy so I'll stick to my modest stash of plastic models.
For more info on those large scale planes, check THIS out. The mind boggles.