You should re-pot the plant several times as it grows. You don't want it to run out of room for it's roots but you also can't put it into a container that's too big because when you water the water will enter the soil and not be absorbed which will cause you all sorts of problems like an accumulation of water in the container that the plant can't drink and which is stagnating, and eventually root rot.

You want to make sure it's one plant to a pot for that reason also, because if one dies or you kill it intentionally (because it's weak, or a male, or whatever) the roots of the two plants will have grown around each other, and the dead one's roots will rot, killing the healthy one.

I would say that your container should never be less than 1/3 the total height of the plant under any circumstances, and in the vegging stage a container that's half the total height of the plant is ideal. By these height examples I mean by "total height" the height of the container with the plant inside it.

Always make sure all your containers have good drainage, or its just a matter of time before you get root rot from built-up stagnant sludge.