I have this silly little habit. First, get the tractor mechanically sound, with no leaks, make sure everything is right. I absolutely hate to finish a tractor, then need to put a wrench to a bolt, it will surely be the first scratch, and can be avoided. Oil leaks or gas leaks can really mess up a nice paint job. Rust can be a lasting problem, I like to go over almost everything, when I can find phosphoric acid, I spray the whole thing with it, that kills rust. If I can't find that, I use a product called 'Extend' available at most parts stores, or naval jelly, the active ingredient in both is phosphoric acid. Of course, when handling any acid take the appropriate precautions. Some marketers will call their phosphoric based products rust converters. That is only true to a small extent. I don't rely on their claim, instead, I use a pneumatic needle scaler, and various wire wheels or brushes, to mechanically remove every last speck of rust I can get at, down to bare metal. Then, use the phosphoric to kill the rust in the pores of the metal, if you don't do that, it will come back.
 Then it goes to the body shop. I don't like to breathe the paints that are on the market today. The last time I did that cost me 3 or 4 days work, and it felt just like I had the flu. Good body shops have the right gear, positive pressure suits with fresh air breathing equipment. For me what they would charge is a small price for my good health. My paint man will allow me to come in the night before, and get whatever prep work done, masking, taking parts off to be painted separate. He does this after the day crew leaves, and I have had him arrange to paint the same evening, so his booth is not tied up long. You could check this out, and find a shop that will work with you. I find I get a better price on the work, if I can get it in and out without interfering with the shops normal day to day business. Which is fixing insurance claims, that is the meat and potatoes of any body shop. I give them the gravy, because all they need to do is walk around it with a spraygun. And I don't have to breathe those nasty fumes. I hope this helps you in some way.
Take care!!!
Andy