I painted my car in pieces which worked out best for me because of booth space and time limits. From what I can tell there is no color mismatching, but that will be determined once I get the fenders and doors hung. I painted everything hanging like it would have been on the car itself. Great thing about doing it in pieces is that you get zero tape lines. The jambs look great and the undersides of the doors look good too. The metallics are what can give you grief but luckily this is a factory color and the metallic flake is pretty fine and lays down nice. Bigger flakes I bet would be more finicky. I tried to make sure I used the same number of coats on each part and the same gun and settings. Relative humidity doesn't change much around here and temps are pretty steady as well. Even the pieces that I had to do blend repairs came out great. I can't see any evidence of a blend.
As to your second question. I shot 3 coats of SPI Universal clear which is a very high solids clear. I wetsanded it with 400 grit. Then I shot 3 more coats of clear that was reduced 10% so it would flow out really slick and reduce any urethane wave which happens when you not a pro with a spray gun yet. Plus the greater number of coats contributes as well. Doesn't really matter much since I begin cutting my clear with 400-600 grit to get things really flat and work my way up to 3000 grit.