Hi, well I would not worry on underwatering vs slow growth as it is to overwatering for slow growth. Atleast if you underwater your roots search for moister and water!! This is why some people bottom feed. Also some people practice watering little and more often but still making sure they bottom of the pots are wet. I like that approch. When I feed I usually use a little less and when I water, I usually water heavier. But thats because I am on a Feed, Feed water routine.
About your lighting, I def think u justified the growth we see. U can use the 400MH sooner than what u did. I look at it on how many crops a year can I get. Small under the MH for one week, well thats hard to say because what did they look like when they went in under the 400MH. But I think they are finly showing some broad leaves and starting to cover the surface area of the pot- That to me is saying that your are finely stimulating your plant to build roots and grow! BTW, u def can keep your 400MH pretty damn close to the canapy. just make sure their is not a 'accumulation of heat', so a fan out take that hot pocket out around the shade and bulb. Maybe keep light one foot away!
About nuts, I would try out vitamax by grotec. Its a 1-1-2 so it has some nitrogen for the fixation of the P,K and it also has some good K value for root stimuli. great supplement for a feed program and helps to round your program out. I thnk u will like it!!Your plants will and if your ladies are happy, than u can be happy!