1) moisture: you dont seem too badly off, but heres a tip: take a spraybottle of water and just mist into the air about a cup worth of water once or twice a day, thatll bump it up pretty fast.

2)nutrients: they sound big and healthy enough to begin being fed a dilute solution at the least. but remember: overfeeding causes more problems then underfeeding, so dont overdo it.

3) light: you say you have a 250w hps lamp. that is very good, and perfect for 2-4 plants. however, hps light is not ideal for vegetative growth. look into buying 30$ or so of DAYLIGHT/COOL WHITE CFL bulbs and wiring at home depot. if you can get about 150w of cfl (600 equivelent), it should be more than enough until you start flowering with the hps.