vertical moving lights, airpot, airfloor or high pressure aeroponics. (Focus on oxygenating roots/ideal root temps, using light footprint w/o hood.)
if you ask me, its a lot of investment for the hpa setup
Good reflective material (this means cleanable stuff, like the polished dimpled aluminum shit)
air filter on intake (prevents dust getting on plants, lights, and reflective materials)
I wouldnt go higher than 600w bulbs to achieve highest GPW, because 600w's have the best WATT-LUMEN ratio, if you look at 1000w's , they have a lower watt-lumen ratio.
there is a huge debate here
yeah dont forget co2 lol