Hey,
I'd go with a 3-5 gallon bucket
After they have 3 sets of leaves and some side shoots, pinch off the new growth on the main stem and you will see the side branches shoot up, wait a week and cut both side shoots and then, if you want to do it one more time you can depending on how much space you have. As it grows you can interweave it through your trellis/net or whatever you use for the scrog.
Your goal is to have all tops above the net level so that the plant evenly distributes it's energy to each budding site. 2 weeks in i pinch off all lower buds. if you did the scrog right no light should penetrate so you won't need those lower popcorn nugs.
As for height I would keep tops 2 ft away with a non air cooled hood and 1 foot with a cooled hood or cool tube.
Height isn't as important as the root system you have built, and how thick those branches are. The thicker the more water and nutes they can carry and the more weight they can support.
By getting oscillating fans on those young plants you will toughen up the stem. Eventually you can get into super cropping and fIM-ing, but I'd keep it simple this time.
