Potisyummy,

Hello and welcome to the best hobby in town!

O.K. lets see.

Workshop bench is 3'x3'x6'

That brings your Cubic feet to 54. Take your cubic feet and multiply it by 3. This is how much Cubic Feet Per MInute that your fan will have to exhaust. In your case you would need a fan that could exhaust 162 CFM. As far as air intake is concerned, this is how I was shown to figure its ratio. Take the size of hole that your exhaust fan uses (probably a 4" fan/4" hole) and multiply it by 4. This is the size of hole you will need to cut for your passive intake. If you want to use an active intake then I believe you just have to match the same CFM going in as you have going out, but I am not sure.

Put your intake low to the ground and your exhaust up by the ceiling on the opposite end of the work bench.

I think that you will play hell trying to keep a 500 watter cool enough to use in such a shor area. Once you get the light and buckets in there you will only have a foot (or less) for growing space. However you could raise the bench up like you mentioned to gain a little more space.

This is what I would do if I were in your shoes.

Lighting

Go to Wal-Mart and buy the $8.00 four foot fluorescent light fixtures that they sell. Buy the 40Watt tubes that they sell also. There are two tubes to a fixture. The fixtures are aprox. 5 inches wide. So you can fit seven of them in an off set pattern in your box. They are only about 3 inches in height, so they will take up virtually no space. You will have 14 tubes in there at 40 each. This will give you 560 watts with 1/4 of the heat you would have with your 500w MH. I would buy 7 blue tubes and 7 red spectrum tubes. Then use one each per fixture. Fluoros and great for heat issues but not good at all when it comes to light penetration.

Strain

I recommend the strain lowryder for you. This is a great plant for stealth use. It is available through Drchronic.com, treatingyourself.com, and a couple other places. drchronic is very fast and reliable.

This strain autoflowers so you will not have to worry about light cycles. Just set your lights for an 18/6 cycle and thats that. They grow to be about 12-18 inches in height, well within your range. They take around 2 months from start to finish. You can keep one male to get seeds for your future grows. This plant will produce around 1/4-1/2 ounce per plant. I have grown them out in the past and my average was closer to the 1/2 ounce side. I did not use fluoros exclusively though.

I think that this is the perfect plant for your situation. If and when you get to grow bigger then you can get different varieties of herb. But I think that with your height restrictions and need for speed, for stealth purposes. This is the way to go.

I would vent the box like I mentioned before. Air exchange is a vital part of growing.

Go with the fluoros, they will provide you with decent results in your cabinet.

Paint the inside of your cabinet flat white, or buy some mylar. You do not want to waste any light. Do not use aluminum foil for reflective purposes.

Try out the Lowryder strain. I think that you will love it. Here is a link to another site that has a ton of info on lowryder. Official Lowryder Fanclub

When growing lowryder do not fertilize it too much, if at all. It does well with organic soil. Maybe a little superthrive, but not much. This strain acts very strange when it comes to nutes.

I hope this helps. If you have any other questions or need me to clear anything up just let me know.

Peace