I don't have to worry about humidity so I prefer planting densely. You probably don't need to worry about damaging while separating them. It used to concern me until I purposely damaged some seedling roots while up potting them. They did as well as the plants up potted with tender loving care.
I am growing some Carbon, Tarasenko 6, Jaune Flamme, Sungold F!, and Arbuznyi plants this year where I have purposely grown two plants in the same root ball or with the root balls planted against each other. I then planted each variety again as single plants. I had two purposes. I wanted to see if two plants in competition for the same space would be stunted or damaged. I also wanted to see if two main stems growing from the same space would increase production compared to the single plants. So far, the double plants are out performing the single plants in growth and total blooms. Some small fruit has been set on all of the plants including the single plants. I won't really know the results until near the end of the season, but to date; the double plants are beating the single plants.
I am also growing four of the dwarf varieties in containers with two plants of each variety in each container. They are doing great and blooming great. They were direct seeded in the containers with three seeds of each variety. I removed the third plant after they were all growing well. The containers range in size from three gallon up to five gallon. I have drip irrigation to each container and haven't been able to detect any difference between the plants in the smaller containers and the larger containers. So far, the variety, Emerald Giant; in the three gallon container is taller than the others at about thirty inches.