No problem with snapping it, people do it on purpose all the time. Topping should benefit you in this case.

Probably doesn't need a new pot yet, but if you're worried about it just check the roots. Wait until the soil is mostly dry, place your hand on top of the soil turn upside-down, and slide the pot off. Be careful not to break up the root-ball.

Eventually you will need 3-5 gal pots, depending on how big it gets. I would also bury it down a little once you do transplant.

For the soil, you will have to fertilize eventually, because the fertilizer in soils will run out within 4 weeks after planting/transplanting. Cannabis-specific nutrients work the best, but you can find similar ones that will work also.