Stealth scrog 400w hps first grow cab questions!

Hello!

I have a few questions about a stealth scrog cab I'm trying to make (I've decided to go the route of converting a desk/cabinet thingy rather than use rubbermaids). I'm new to growing but have already completed my first little CFL veg cab, got a couple bagseed sprouts to pop up, and I'm now moving on to a HPS flowering cab.

I'm at a bit of a standstill now after actually obtaining a cab to use because I'm not sure what size of plants to plan for. The only thing for certain is that I'm using the hempy bucket method, and I want everything to fit the output of a 400w hps. I happened to stumble on one for free so since it's the most expensive component I thought I'd build around that.

This is what I'm working with for sure...
-bagseed indica
-400whps
-1.5x3x4ft (or possibly 1.5x3x7ft)
-salvaged squirrel cage fans

And here's my questions!

• The top section to be used is about 1.5ft x 3ft and 4 ft in height. There is also a lower section that I could extend the growspace into which would simply add another 2.5ft in height. Given that I only have about 6 sqft to work with, is there any sense in that extra height? (If not, I would make it a separate veg area)

• Does it make sense to grow in ~12ish 2 liter bottles when I have 3 ft of room for them to grow up into for a scrog? Or should I use bigger containers with less plants? (hempy method)

• Is a 400w hps suitable for this size? I was originally planning on something smaller but as I said, the 400w was free.

I have no camera so all I have are some really crappy phone pics of my first little box and my lil' babies. I'll get a real camera tomorrow and take pictures of the cab.

Thanks in advance for the help!

Another quick question to add on - does it make more sense to have your carbon filter on the intake of the cooltube inside the growbox, or attach it to the exhaust outside the box?

The exhaust.
Try to get it to pull air trhough not push air out.

Wouldn't putting it on the exhaust side make it push air out?