okay. i want t know about how well your ducting works in the end. I think you will end up having to play with a lot of things.
1-You want to think about smell control.
2- Get the ac hoods on sealed systems. I think since you say you live in the desert, take air from the house, through the lights, then outside. no need for smell control if these are sealed well. 2 lights on one 8" fan will probably be okay but keep all ducting straight as possible(use rigid ducting where viable), short as possible, and same size as your fan. length of runs, bends, flex duct all play hell on CFM.
3-A/C units are usually used in rooms that dont use fresh air cooling/exhaust. Decide on one or the other i think. A/C also takes air in and spits smell out so You would need a scrubber running 24/7. This is a solid form of smell control though. This can be a good option. I think you should seal this room well and insulate it well. Air cooling the hoods with one fan and getting a nice 8" carbon filter to use as a scrubber with the other 8" fan. (i have 2 of these 8" valueline fans, i like them) cooling room with A/C and oscillating fans. You are going to have to set this up and run it dry(no plants) to get temp readings and make adjustments from there