Depends on size of lead. Small jigs only take a couple seconds but when you dip you’ll know if it was enough or too much. I use an alcohol burner and they may be slower than a propane torch. I don’t use a fluid bed and have good luck stirring or fluffing the powder every couple jigs.
Too much heat it will boil or cook.
Not enough and it won’t coat.
It’s a steep curve.
Haven’t heard of a primer for them. Some colors need an undercoat of white to look right though.
just my 2 cents.