The quiet compressors are a real boon, but I used paint brushes for this.
There is no prep necessary on veg tan leather.
Acrylic won’t stick to oil tan. I’ve tried and it cracks or peels in a very short time. Chrome tan is different, but usually it bends beyond the limits of flex in the paint. If it’s flat or doesn’t bend much, it will stick.
you do not need to wait between layers if you’re painting with a paint brush and you want to blend colors. If you want to paint on top of that blend, then it needs to dry.
if you’re air brushing, it’s best to let coats dry completely, as it’s a different process, but there are techniques where you mix colors while wet.
acrylic paint = acrylic finish. Other finishes will lift paint or dissolve it.
Acrylic paint has an inherent ability to flex if its thin enough. Thick paints suck at this, which is why I always use pro grade paint. They can be pushed further than cheap paints. The liquids that carry the pigment are superior to craft level paints.