just as a suggestion of something to look into. You could do an ac unit that recirculates the air its cooling(would also act as dehumidifier) then get rid of intake and exhaust and make sure your light venting is 100% sealed. just talking about doing that makes me jealous your intake and exhaust ducts would then come in handy to cool the ac unit..how far along on this are you some pics would be nice.

All that being said if you decide to go with a vented hut you could hook the venting up to a thermostat instead of timer and make it so the co2 wont try to maintain 1500ppm while the fans are running.(I am not sure what would be the best way to control humidity then)

I don't know about you but to me the sealed route just sounds so much more pimpin. i don't really have experience with this but i do have a background in related fields. more opinions would be needed for sure i was just tryin to help.