1.co2- you can get plenty of co2 for this size grow from the environment around. You need to get air from the circulating in and out of the tent. The fresh air you pull in from outside the tent will have co2 in it for the plants. Fresh air exchange is what this is called, and its very important. Most people put a carbon filter on the exhaust air that blows back into the room to prevent smells. The intake side a shouldn't need one.
2.heat-good fresh air exchange will help drastically with heat to start with. Moving the hot air out of the top of the tent and pulling cooler air from the room outside in the bottom. Then if you cool (or heat if needed) the outer room it can help control temps even more
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3.Nutes-this is a highly debated topic, and I usually suggest trying different things yourself to see what you prefer. Personally I've tried lots of methods over the last 13 years, and I feed till the day I harvest. I also don't feed heavy to start with. I give the plants what they want to be healthy and don't try to give them any more. I have tried flushing, and reducing feed near finish. Frankly once I learned how to dry properly I never saw a difference with flushed or not. The last 2 weeks of flower are when the plant is swelling up and putting on lots of weight. I personally hate to starve my plant during that time.
4.lighting- also highly discussed, and I've tried a bunch of stuff. I usually run 18/6 during veg, I like the idea of giving the plants some rest time. I also noticed more stretch during veg when running longer light cycles. I do mean stretch as well, as in distance between nodes. The plants would produce the same number of nodes, but farther apart, and that's not what I was looking for.
I've tried some different light cycles in flower as well. For many years I just ran 12/12 because I've never noticed a drastic different in growth in the things I tried. However the last few years I've been running 13 dark, 11 light in hopes to trigger a faster flower from higher auxin counts. I'm not gonna say its made a drastic difference, just another thing I'm playing with. I've read qoutes from breeders that talk about getting optimum growth from non 12/12 cycles, but they didn't say exactly what they used.....