Some technical questions:
How many coats of primer on bare metal surface?
How many coats of paint ?
Should I add 1 or 2 extra coats of clear laquer for paint protection ?
Match your paint types (and brand if you can. brand alone is no guarantee though) Most botched paint jobs are from paint compatibility issues, putting too hot a paint carrier over top. I don't like the thick 2x finish on anything but tinplate. The "plastic bonding" paint I've bought was like painting with foaming bathroom cleaner. It's thickness cured was unreal. It fisheyed on itself and it was like sanding soap...beware; even on lawn furniture; beware.
Laquer is easiest due to dry times. It is thin, so retains details, and blends coats very well as the carrier is so hot. Enamel is rock tough, also kinda hard to apply in that the finish coat being an even wetting is how to achieve perfection.(esp. gloss, not so much satin/matte)
Lacquer is "hotter" than most enamel, topcoating over other paints it needs to be done carefully, if at all. The many years of cure and stability of the enamel paint help us topcoating the old enamels. But on fresher paints, there are often more issues.
Some paints pull hard on their surface as they cure and try to lay flatter. So a hard puller on top of a soft paint , or a carrier that might penetrate an old coat can cause "gator skin"/ top crackle, or actual cracking of bottom coats as the bottom coat shrinks more from carrier exposures, or structural bonds are destroyed chemically.
Light coats stop runs. Runs means you are in too much of a hurry. "Ten" light mistings then a good finish coat would be great. Mostly, we all try to squirt that much in one or two passes, lol. Don't confuse the wetness with color, the wet sheen will go away and color will blend. Satins blend well...as long as you shook the can often.(try to get the finish coat out of one can.) Experiment with misting to get a solid color and as tack coats against runs, instead of using wetness as your guide.
Also "fish eyes" are normally contaminants. Wash it and dry it well before painting. Wiping well with spirits or thinner to remove oils just before spraying is a good idea too. Warning, with all the lubes today, soap and water doesn't always get to embedded silicones and molly lubes. With those two examples, you likely need to strip it and give it a solvent soak.
Build color in mists, corners & edges first; "the cut". Use a " tack coat" when beginning, and on the second to last coat, to give the finish coat more stability against runs. A tack coat is a light misting let to set firm before top coating ( but not to dry.15sec to 20 min depending on paint)
I leave my numbers alone. Dont mask numbers with tape. Cut paper to size to protect then apply tape over that, feather the cab sides to the #mask, keeping it light so heavy ridges dont form. Mask liberally over the headilght, etc. and touch up around it later with a brush. The gap between lens and shell looks like crap if it fills with paint. That goes for whistles, bells, stanchions, etc..
Don't forget this is also your opportunity to do a one off. A black repaint and a color repaint are both still repaints.
I think when I repaint next, a Prussian Blue metal treatment will be in order.