T4 has some good advice on the light leak, and that is pretty much what I do to "light proof" door ways. Another thing is to build a "light trap" just inside the room where the door opens. I hang Panda from the ceiling to the floor just around the door way and use a Tarp Zipper to get in and out. That really helps cut down on light leaks with higher wattage rooms.
Your pic shows excatally what I was talking about, but I too agree that it MAY just not cool all 5 lights enough. As far as pushing/pulling, I do not think it will make a differance as afar as one cooling better then the other.
weather you pull air from the 600 side or the 1000 side, it still goes thru all hoods right?
I allways think it better to pull, and the MAIN reason is if you push, you WILL push small amounts of hot air into the room. Period. The MINIMAL leak you MAY have by pulling air and having "stinky room air" enter the hood cooling system is nothing to worry about and it will not be a cause for alarm or smell.
With the hoods you have, that glass will suck wight up to the foam seal around the hoods, and if you pushed air bro, it would try to seperate the seal and force hot air out, IMO.
The 6" room exhaust is the blower you need to have tied to a Carbon filter.
WORST case, you will need another blower and string up 2 of the 4 600's to one blower, and the other 2, 600's and the 1000 to one.
We are rolling into winter, so I think you can get a couple of clicks off before you really have to worry about big heat issues, so I think you can run with that one 8" for the next few months.