I'm certainly no expert on painting, there's plenty of better qualified people than me to answer your questions..... but right or wrong, here's what I did.
These bits are off my Lawn Ranger as descibed in this post:
http://whtractor.15.forumer.com/index.php?showtopic=3240&hl=
A lot of the smaller pieces have been painted with rattle cans, but the toolbox, fenders, hoodstand and these bits today where painted with a gun. Its all been Valspar "Restoration Series" paint from TSC (both in the gun and in rattlecans). I used Hardener with the gun Primer has been Valspar sandable grey mainly, or High build primer from NAPA (dont remember the brand) or an etching primer also from NAPA. All the primer was done with rattlecans (apart from a disastrous f-up on the hood when I used a gun and ended up taking it back to bare metal and starting again).
This tractor was really rusty with a lot of pitting, so it was taken right down to bare metal, run through an electrolysis tank, small parts were blasted, a skim coat of filler on the worst of the pitting. The primer was wet sanded to 400 grit most places, the hood wet sanded to 800 grit.
I put 3 coats on the non-visible bits and 4 on the tops, about 20 minutes between coats. It was dry in a couple of hours, but it stays pretty soft for a couple of weeks (at least it did in Summer time). With the cooler weather maybe it will stay soft even longer?
I think I'll try buffing the orange peel first, if that doesnt fix it I'll try wet sanding. If I still dont like it I'll rub it right down and take it to a real painter!
As I said above, there are some very experianced painters here who could answer your questions better. I'm just a hack!