from what I know of bonsai you need to prune roots and what I know of mj its a tap root so you need a deeper pot than the average bonsai that has spread out shallow roots also roots relate to the size of the plants canopy
I try bonsai with an expendable sample first and cycle clones or breed true seed if you can until i knew it would work for the strain you were targeting...
The smallest I've done is the bottom of a 2 Litre soda bottle with it's top cut off.
I love them because they are deep but narrow so I can just pop it out, trim the lower roots and pop them back in.