I cant comment on the ebb/flow system as ive had no experience with it, plants per sq ft ultimately comes down to strain (indica/sativa), how youre going to control the growth of your plants, maintanence and floor/wall space for all your control systems, air circulating fans, extractor and fresh air fans, resevoir, size of lamp, distance from plants etc etc
I use T5 flourescent for seedlings and veg and HPS 600W for flower. If your cloning youll need 2/3 rooms for different environments, light settings and light distances which means more control systems, more light systems and timers etc
If the ebb/flow system is hydroponic then PH levels are critical as are PPM so yes regular checks needed. Plus digital meters for PH, PPM and PH adjusters. Speak to your local hydro shop for nutrients. Your bulb rating, number of lamp units, ballast units, contactors and timers will come down to calculating how much space you lose in the grow room by everything you need to control the environment then see whats left for plants. Choose your wattage from there but ultimately the more juice the bigger the yield. Fresh air is vital as it contains CO2 which is obviously vital to the plant, so provided you have a fresh air supply and an extractor fan big enough to get the hot air out your ok without CO2 but the more CO2 during flower the better and yes turn the fans off at the same time so the plant can use the CO2 d0ct0r