for simplicity i would use a starter pot and a final pot and nothing in between. but there are a lot of growers who believe in the power of "upcanning" or multiple transplants. the thinking is that the roots get stimulated and after a brief recovery period take off harder than they would have without the transplant. i'm not sure if i believe in that but i've honestly never tried it. also remember that each time you transplant into fresh dirt it's essentially like adding fresh nutes, so you have to be aware and let them use up some of the new stuff before you go dumping full strength ferts on them.