Painting Logistics

I was looking at the picture of the Ebay cart that Pam posted, and wondered about the logistics of painting Ebay pieces. Do you do a single piece from start to finish? Or do you have a few going at once?

With knowing nothing about airbrushes, is it easiest to paint all the (insert color) on all the pieces you’re currently working on, and then switch to the next color? Or does that rarely work out because they’re all so different that when one piece needs one color, the other pieces aren’t ready for that color yet?

Thank you!