Your 200 liter container will almost hold enough for a 1000w DWC grow.
Your pH swing will be too slow for an optimal grow if you fill it and use a 400w... I prefer around 45-57 liters for a 400w DWC.
If you're running 'drip' through a medium... you can cut down on those numbers a bit for each light.
Keep it Clean!
p.s. I usually don't click on off-site links... would you mind uploading that to your gallery?
The metal will retain and radiate heat. Rooms with hoods hold more heat than those without for that reason. Cooltube that bulb and exhaust the entire cab via the cooltube. Passive intakes open opposite of the cooltube opening/scrubber. If you're displacing the entire cab every couple minutes it won't matter what kinda heat your lights pumping.
400w for bud density 250 for gpw efficiency.
Keep in mind some strains bleach easier than others. This is a nice vert donut mini-cab idea. Run chicken wire or similiar all around the inside will to train plants back.