Like with any job 90% of the finish comes down to how much prep work you do. Then when it comes to spraying as long as you're following the basic steps I think the main thing you want to avoid is runs because they are a pain to fix. Orange peel and rough spray patterns are easy to fix as long as you put enough coats on and you don't mind doing some sanding.
With auto paint you don't want the final finish to be too thick because panels can flex easily and a thicker coat will split. But on a solid guitar body I don't think it matters. Spray as thick as you like and you don't have to worry about going thru to primer when you sand/buff. Once you've sanded it enough to remove orange peel you can buff the bejeezus out of it to get a mirror shine.
And when it comes to candy I reckon the thicker the better. Light is reflecting through that candy coat and hitting the silver underneath then coming back out again. At different angles you get a much wider contrast in shades. It can look like an actual candy apple (toffee apple for us Aussies) dripping wet with some sweet coating over it. Thin coats I reckon don't look much different to a pearl or mild metallic finish.
Another tip... or idea... airbrush some faint dark patterns on the silver base coat before you put the candy over the top. Don't try a gold base coat I already did that and it looked rubbish.