Nutes will lower the ph so there is no reason to ever ad acid to nutes. The top of the plant produces the largest cola and is where the plant has the highest consentration of growth horomones. Since you only have a limited space more plants with single colas will get the highest yields. I would make two cabinets if you can and grow smaller plants. If you grow a mother start your clones into bud at 4 inches. As far as scrogging goes I hope you like trimming tiny nugs but in my opinion I think it is a pain that diminishes yeilds. Co2 can be made with sugar yeast and water. If you can make it out of sheet metal it will stay cooler with a small space. Also will putting the ballasts on the outside of the cabinets. I would put in one 400w Mh and one 400Hps in each cabinet. end to end not side by side. Paint the insides white flat paint.
One love
c