I'm a novice, but I would guess that if they end up being different sexes or if they grow bushy that crowding could become an issue. I had two to 3-gallon containers in soil for a while trying to save space, but put them back in separate containers within a week after I saw how fast they were growing. Plus I didn't want to risk accidental seeding.

At first transplant I tried worm castings mixed with Supersoil, Perlite and a scant amount of charcoal chips and switched from HPS to a MH conversion bulb. Within a few hours I noticed an improvement. I used Peters 20-20-20 mixed at household strength. I once had a roomate who used guano for her houseplants and the whole place smelled like landfill that was eaten, puked up, re-eaten then defocated onto a rotting corpse.