Your out take will be dictated by the amount of intake or else you'll implode the tent ;p. Open all the vents and put a feather (etc) on one, if it sticks firm to the mesh then it's not getting enough intake or the out take is just too high. So then you'd have to open a lower vent hole if you have one.
Dehumidifier won't hurt but the problem you have if they do get over crowded is the mid canopy will have little airflow/movement so over lapping leaves will trap moisture along with the sides of the tent. Loli popping does seem like a safety choice in this situation where as normally it's a divided topic. But I dare say most people against loli popping would suggest that if you didn't cramp plants together you would not need to do it in the first place. On top of that, if your plants are say 1.5f tall and you loli pop, your lights can penetrate that far so you are losing weight. So then you are kinda removing the point of doing more plants since you'd likely get similar weight by putting in about 5 less that have more space and don't need to be loli poped (don't quote the numbers ;p). But, defoliated plants that have mostly big tops will be easier to trim so maybe you will like that idea.
Have you done a test run with all 600's going?. It's going to be a lot of heat and if you can't maintain lower flower temps through out the 12 hours you may be better off going with 2. If your out side humidity is high/spiking yet you are forced to suck in lots of air due to heat it might be a problem. I don't think a huey would be able to keep up with that but somebody with more experience in that situation could tell you more. You should also closely monitor your night time humidity, the setting on out take may need to be turned up/down or w/e your environment requires. One would imagine a low setting with dehumidifier would keep it right but again somebody with more experience of that issue could tell you.
Anyway your plants look lovely and you look like you've done a lot of research so you'll probably figure it out regardless. What you really do need to consider though is that by the time you realize some buds are starting to rot theirs not much you can do about it other than cutting it off, at that point it means your environment has failed but hopefully you don't lose much. Just make sure you stick by your guns of removing plants if they get too crowded after the stretch. Post pics at that time if you like I'm sure people will let you know if it looks risky.
