600w lights will do approximately a 5x5 area. if you had three you would have ok lighting but i think you mite be stretching the width with your 6.5 area. if your want to get serious you would go with six! two rows three long! then you would have tons of light, but you will have to vent with 6 inch vented hoods,ducting and fans!! 50 plants? yes i think thats practical but what you have to think about is, are they going to be reachable when they are big and flowered out? will you be able to water all of them? how about spraying them for mites and what about keeping control of mold. these are things you always have to think about, so you want to be able to get a good look at all of them so you can check the leaves. even the ones in the back!