I have been doing custom cars for years. The first ones I did I used all Dry Transfer lettering. 35 years ago.
Now its all done one the computer and printer. I must tell the truth my wife Michele makes this happen for me. I let her know what I would like and she does all the work making the stickers for me.
I use many different cars. They must be smooth sided. So many times I remove all the rivets etc. where the sticker will go. I use Shipping labels the true block type so nothing shows through the sticker.
Most cars I do not repaint I find a car the color I want. I really like MTH Hi Cube cars. I take the ladders off and after the car is stickered you put the ladders back on and it makes it look like the car was pad printed.
Sounds Easy Have Fun. Just remember these are paper stickers so when I handle the cars I never touch the sides. But my wife saves them all so if I mess it up I can always print a new side.
A few cars I have done .