disagree, 2 600w is plenty light for a 5x5...that guys trippin
Always trippin...
I think you have the right idea with the 600w systems but I really think you should consider going vertical in your tent if you're going to use them. This will adequately and evenly light the entire area. Stack one light right on top of the other. You could consider actually getting the 600w Hortilux HPS and a 600w Digilux Metal Halide and go for a really complete light spectrum. Using cool tubes would allow the plants to grow within 1 foot of the bulbs, so you're really only losing 4 sqft while gaining the entire vertical area of the tent.
When it comes to cuft of canopy nothing beats vertical systems in efficiency. I know that's what you are going for.
How you do this is up to you. There's a lot of methods. A simple one is to use shelving units around the light and put the plants on the shelves. Then you train the plants forward (because there is a shelf above it) into some trellis netting. then you basically weave the plants into the trellis. You can use nearly any method of growing in vertical systems.
You can also just grow nice big tall bushes that will be full of thick resinous buds from top to bottom due to the even vertical lighting.
Whatever the case is... I think you should seriously consider vertical 600's if you're not going to run a 1000w system.
The heat from the 1200w of lighting is the only thing to worry about really. Of course you'll need to be regulating the intake temperature, the room temperature, to beneath 72 degrees or so. Easy to do in the winter but impossible without AC in the summer time. The lower intake temperatures will help keep the tent interior temperature lower.
Figure you have a 160cuft of air in that tent you need to be moving. If you can manage to efficiently use a 180cfm 4" inline fan that just barely might cut it. Including an axial fan in one of the tent intake vents would probably REALLY help the interior stay cool as well.
The problem you have with the filter is that it isn't rated for a 6" fan. So, if it turns out the filter and a 180cfm exhaust and 6" axial intake fan aren't moving enough air then you spent a bunch of money and now need all new shit.
It is probably better to get a 4" fan for the filter and place it somewhere in the tent on it's own independent thing. I'm not sure how great a job it will do on some stanky ass plants, but it would probably be okay for most average grows... but don't quote me on that...
It is good to see another grower getting into the game.
Sounds like your entire system. Once completed... depending on the method and nutrients you choose... Probably $2,000 on the lower end. The first harvest will make that entire investment back in spades. From that point on... Nothing but money in the pocket.