In addition to all of the great information from others, a paint you might want to try is a Rust-Oleum product. It is designed to be used on indoor / outdoor projects. I used black but they have a few other colors. It dries with a fine textured finish in one coat. I suggest that if you use this that it would be the last thing you do on the body. I don't think you could mask over it and not have paint get under the tape. If you use a white color it could make a good base for lighter colored tops.
I have also used Modelhaus bodies and other conversion parts and have never been less than 100 % pleased with them. The interior looks great, but I wonder about the holes in the floor. Are they maybe for mounting bucket seats ? The wheels look more like a standard wheel that would have a hub cap covering it. The suggestion of the "police" style wheel would make the most sense. The pictures I have seen of restored 1:1 cars have a wheel with the vents as seen on those wheels.
Very nice accurate body mods to make a 210 model. As an aside, the six cylinder engines were painted blue, as in "The Blue Flame Six". Nice to see the extra effort on the interior to make it right also.
Most of the kit tires have an almost to shinny appearance on the sidewalls. I think that the flat clear from Tamiya gives a more realistic look. I have also found that if you have used any type of white wall or raised lettering treatment the chance of smudges are minimalized. I'm finishing a model now that I'm using the reissued Good Year tires on. On a previous build I some how whipped off a couple of the letters on the tires and really lost the look I was going for. This has not been a problem since I started doing the flat clear. Try it on a spare tire and see what you think.
All great ideas. Another is to pickup some ladies finger nail sanding sticks. They are usually very inexpensive and most drug store or even the market carries them. As pointed out the very fine ones if you're doing the side walls. Another thought, After sanding the tread mask it off with tape and lightly spray flat clear on the side walls.