If you're dealing with full sized plants 3-4 feet finishing height ideally you should put under one 600w light is 3 plants or 5 plants per 1000w. When plants are that size they need at least 200w of light each. If you don't have enough lighting you'll have some finished top colas and totally underdeveloped pop corn buds. These may or may not need a few weeks extra to finish or they might not grow properly at all if the plants are really dense. Putting too many plants under one light just lowers your total yields in the end. You really need to balance things out to get the right amount. Also too many plants cause issues with molds, humidity, and poor air circulation. Not to mention poor light usage/penetration.
More plants doesn't=higher yields.
You'll need an area larger then 2x4 if you plan on using 1000w lights. My hoods a lone are pretty damn close to 6 feet long end to end.