1- Skip the polishing kit for now. It is really not necessary, especially for your first few builds. It is a fantastic way to add complication and frustration.
Concentrate on putting the paint on in light, even coats. A dozen mist coats always beats 2-3 heavy 'wet' coats. Use the hot water trick to warm the paint cans before spraying- it makes a terrific difference. (The spray lacquers you're using are Tamiya, I hope?)
Also, do not try to apply the body paint all at once. Don't even try to put it on in the same day. Give it a mist coat or two, and then wait an hour before the next mistcoat or two. Patience and technique will take you far. It just takes some investment in time. Bodies cannot be painted quickly (at least not well!
).
2- Acrylics are fantastic for the rest of the car. I wouldn't recommend anything else.
3- Usually no. It won't be visible, and therefore isn't worth the effort or paint.
4- Absolutely. You
must wear a respirator when spraypainting. Open the garage door, also.
Sounds like a good kit to start on.
Welcome to the hobby!