1st of all HI
lol A random thing to post in my thread but hey! lol, I'll help you (This once)
Ok Yes the design would work BUT.... you'll need an in line fan that moves air fast and is quiet a SYSTEMAIR in-line fan should do the job @ 5 or 6" (if you plan on using HID lighting ie MH/HPS for the size of the setup I would be more inclined to tell you to use either a 250w Envirolite/Envirogrow light or A 300w Envirolite (CFL) since CFL dont put out anywhere near the same ammount of heat a HID and you could getaway with using a 4/5" low powered in-line fan... much quieter and it will cool the CFLs nicely!
You will need an air intake fan, and an air filtered outtake, so 2x CPU fans will do...1 at the bottom left drawing air in and 1 right at the top blowing air out, wire them together and attach to a timer, do this for your light too (on a seperate timer) and have both timers set the same. Ie Lights on.. Fans on..........Lights off.. Fans off! Job done whilst in veg smell wont be much of an issue but give it just over a month and the smell will get stronger, be advised its a good idea if not essential to get a carbon filter for your outtake fan as this will keep you room smelling normal.
The moving of the shelf seems like a good idea, just remember if you hold your hand under the cooltube n it feels hot....too hot then the plants wont like it so a bigger fan maybe needed! BUT if its barely warm and the ambient temp of the room id 26oC there abouts the girls will be loving it! 21oC min 28oC Max is what I go by and as close to 26oC as possible the rest of the time
Plants need fresh air, it helps them grow and bringing in fresh and blowing out old also prevents mould and other nasty thing that can pop up n piss you off in your grow room! So although you light tube would be seperate...you WILL still need a seperate air in and out to keep your girls healthy, Obviousley in veg it 18/6 - 18 Hours of light 6 Hours of darkness (complete darkness) and in flower 12/12 - 12 hours of light 12 hours of complete darkness! And you need to keep the soil (if your using soil ) - DAMP not waterlogged and not bone dry, you'll need to PH balance your water you give them PISS YELLOW On the PH TEST is the preffered test colour about 6 - 6.5 then low quantities of nuitrients that are intended for use in soil grows.. (NOT MIRICAL GROW!!!) lol a grow shop/site can assist you more on this
In this setup I would leave CO2 alone...its do-able but for the effort/expense its not worth it good nuits..good light and good air will provale here Thing to remember is plant can grow big.... If you put them into flower early (6-8") they'll be fine in that sized setup if you wait till they are 21"+ then they'll get pretty big ie sometimes 40 - 50"+ and bigger than that too, So my friend
......With a bit of adjusting this would work fine but from experience double the height of the unit, when the plants get bigger and fill out there is not as much air movement in the grow space and the plants WILL SUFFER expecially if its your 1st go and your learning...Hope this helps dude - STELTHY