It could be a strength issue. I'm not a metallurgist so I'm just guessing. Casting might add some strength that's not there for billet because I see the centers are cast but everything else is billet. If you cut a billet center, i don't think anyone would know the difference if its polished.
Yes, really nice. Attention to detail is top notch. The bodywork is seamless, and the paint is awesome. Even the application of the carbon fiber decals is perfect. I know how much work went into this, and I applaud you!
I will prob always use cans for some but airbrush is on the wish list. I'd like to try my hand at some detail painting and airbrushing is the only way to do that it seems.