new 400w mh/hps grow

i have a grow area of 2x4x7 im currently growing 4 purple ryder from joint doctor,
they are all siting in 5gallon dwc systems, they are 3weeks old and i was wondering if they will get bigger soon cause they seem to still be in seedling form.
i think the reason being i didn't feed them for 2weeks from sprout i read somewhere online to feed at week3 grow nutes(3 tbsp). when i fed them last week i also moved the light 2ft6inch from the tops of the plants. i got a 20in box fan blowing on them 24/7, the lights is 18/6.

i was wondering how much yield should i expect, how much should i feed them each week and how many more plants can i fit under that 400w mh im planin to by more seeds i wann know what u recommend.
AND THANK YOU

First off your not even in the right zip code for where this should have been posted, should have posted it in Hydro section. Before you do that let me save you some time. Go to the Basic Growing section and read. Then go to every "sticky" that has anything to do with how/what/where you are growing and read that. Since you did make an effort to ask for help (even though this has nothing to do with Advanced Techniques) I'll wave my magic carrot and help a lil.
1) 5 gal DWC system. ok that could be individual buckets or your trying to do them all together I dont know but if you have not been watering from the top, all the bubbles in the world wont help from below. Must water topside down until roots pop out and head for water.
2)Light is WAY TO HIGH!!! Even a 600w hps light would be about 12 inches. Light that far away on young plants they wont grow.
3) have no clue what nutes your using so no idea if feed is even close but I can say if it was more than half strength then thats 1 for the "Ooops" category.
4) using a 20" box fan for air movement kinda scares me a lil, I'm just praying it is not aimed directly at them. Would be like using an NHRA Jet drag car to light a blunt.
5) Personally from sprout till about 4 weeks old (min) I have them under a T5 24/0. A plant doesn't have enough foliage to store energy for night periods yet. Think of the leaves like solar panels.
6) to be honest plan on 1 hermie, 1 to die and maybe 1/2 to 3/4 an oz off the other 2. 4 is enough under that 400W and I hope you have an HPS bulb to flower with.
Lastly I'll give you the best advise that anyone will ever give you ............................... Don't rush things!