The idea is to use a small pot to start and gradually increase the size as they get bigger (not allowing it to get rootbound though). Why? Well, the lady will use more of the soil up than if you were to put it in a bigger pot to start with. The roots will move down and to the sides of the pot then chill and soak up water. You DON'T want them to be root bound though.

As to whether or not you should repot or not, I don't know. If you are to do it, I'd do it ASAP, before they get further into flower. I transplant once sex shows, so I technically transplant in flower but a lot of people don't.