The bigger the tent, the more plants!
Still, with a 4 foot x 4 foot, one big scrogged photoperiod plant would be my choice, rather than trying to cram in multiple plants.
And yes, the biggest factor is the light quality.
These package deals have everything, but compromise by trying to keep the price down by having mostly mediocre everything.
You end up down the track upgrading your lights, your filter, your fan etc so in the end you have to buy practically everything a second time.
It is probably better to "buy once and cry once", buying all/most components individually and buying better quality components the first time round. This may take longer to get going, but will help you to grow better plants by having better quality equipment, and equipment that lasts too.
Hope this helps,.........
Organoman.