scrog will probably give you the best yield and if you use clones at 1 plant per sq ft it doesnt take long to fill the screen and most of it will be filled after swiching to flowering, your flowering room is a little big for a 400 w hps you might consider updrading to a 600 for better results.
you could easily use soil or a hydroponic setup for your grow meduim either is fine if its your first grow you may want to do soil atleast partly just to keep things simple such as starting from seed in soil and after sexing take clones and install in a hydro system.