You can start it in the biggest pot you'll think you'll need, usually a 5 gallon but you can go bigger if you want.
Most people start small because they plan on transplanting 3 times from start to finish, Transplanting gets new soil involved and gets the plant back into a growing spurt because the roots have new room to expand. That's about as simple as I can put.
Like I said, you can start in one big pot and never worry about changing pots during your whole grow and alot of people do it that way also.
Good Luck to you and what you decide !!!!