Having problems with brush strokes...

I've been painting parts and panels for my Tamiya P-51D Mustang's cockpit, and with colors other than say, black, I'm having serious problems with the paint finish showing clear brush strokes. It looks horrible and I need to figure out what I'm doing wrong.

I'm using Tamiya's XF and X line of Acrylic paints, and up until today have not tried thinning them at all. I got a bottle of isopropyl rubbing alcohol in attempt to thin the paints, but my effort to mix about the paint and thinner in a 2:1 ratio failed when I dumped in the isopropyl a little too fast. Even with my uber-thin paint with numerous coats, the brush strokes of the original job still show. Here are my questions:

1. What's the best way to get a nice, smooth finish if airbrushing is not possible (i.e. for small interior parts)...or, do people usually airbrush everything with the help of masking tape?

2. What's a good thinning ratio for doing small pieces?

3. How do you guys usually mix paints? I got a shot glass and some toothpicks and let the paint drip in off of the toothpick. I really wish I had an eyedropper or something--I think it would work far better and I would be able to measure quantities as well.

Thanks,
Benedict