With a 4x4, I think 4-6 plants is a good amount. I wouldn't do more than 6 unless you plan on keeping them really small, just because it gets difficult to reach the back ones after they get big and everything is flowering and sticky
If you're trying to keep things low heat and low electricity for the vegetative stage, a High Output T5 is actually pretty effective as long as the plants are under 1.5-2 feet tall or so. You probably won't need to do anything to keep it cool as long as there's good ventilation in the room. Plants aren't as fast-growing under a T5 as they would be under an MH or HPS, but it gets the job done!
The only problem with a really big tent is if you want some plants to be vegetating, and some plants to be flowering/making buds. Unless you're growing with auto-flowering strains, you'll need to be able to keep your flowering plants in a completely light proof space so they never get any light during their daily 12 hour dark period. That's the "signal" that gets them to make buds, and if they get light at night (even a tiny bit like a blinking indicator light) they may start reverting back to the vegetative stage.
But if all the plants are going to be in the same stage of life, you're better off with a big tent instead of two individual tents since they'll get to share some of their light with each other. Just as an example, two 600W lights next to each other will produce more than two 600W lights on their own, since some of the light that would normally get lost to the walls gets picked up by the other plants.
If you're trying to keep things low heat and low electricity for the vegetative stage, a High Output T5 is actually pretty effective as long as the plants are under 1.5-2 feet tall or so. You probably won't need to do anything to keep it cool as long as there's good ventilation in the room. Plants aren't as fast-growing under a T5 as they would be under an MH or HPS, but it gets the job done!
The only problem with a really big tent is if you want some plants to be vegetating, and some plants to be flowering/making buds. Unless you're growing with auto-flowering strains, you'll need to be able to keep your flowering plants in a completely light proof space so they never get any light during their daily 12 hour dark period. That's the "signal" that gets them to make buds, and if they get light at night (even a tiny bit like a blinking indicator light) they may start reverting back to the vegetative stage.
But if all the plants are going to be in the same stage of life, you're better off with a big tent instead of two individual tents since they'll get to share some of their light with each other. Just as an example, two 600W lights next to each other will produce more than two 600W lights on their own, since some of the light that would normally get lost to the walls gets picked up by the other plants.
