Be careful, their feeding chart is very strong. Start with 1/4 tsp per gallon. Feed every other time, moving up 1/4 tsp per 2 weeks.. 3/4-1 is the most I will feed.
About 6 oz for my bigger one with 50 days veg (pictured)
3oz for my small mother
and 1oz per 8inch clone.
I top my plants a few times, snow white responds very well to topping.
For the molasses, you can use 1 tbsp per gallon of water
400 is not enough for a 4x4. Try a 600 or a 1000.
I grow in a 1meter x 1 meter tent and have included a picture of my 7 plants in there. As you can see, it's really crowded and unless you know how to prune well, i would do 4 females.
You mean before flower? Are they sativa or indica? Max height?
There is no set height of when you can flower. Most of my plants enter flower between 1 and 2 feet. I have 6 ft to work with though.