Nice work.
The intake fans are actually recommended against since there is a likelihood of pressuring the air in the cabinet and any leaks would be unfiltered.
Also, for a little more money you can put in 4 or 6 cobs for more even light distribution...
If you have decent access to the entire area, 1 square foot per plant if you flower when they're small. I'll run plants at about 2-3 square feet per plant but I mainline mostly...
I only do the autos that come free in the pack. Personal max auto record of just over 3 ounces and a minimum of 13 grams. Average under an ounce, they're just not worth the space for me.
A 4 foot tall vegged plant is ridiculous. Put them into flower at about a month or a foot to a foot and a half tall.
I'm not a big fan of autos, they're generally not recommended for newbies.
Speaking of newbies, there's a whole section here dedicated to rookies and all of your questions have...
4x4 can easily hold 4 plants, allowing you to perpetually harvest one every 2 weeks. The small tent can be used to veg and start seeds, providing an endless supply of vegged plants for your flower room. Perpetual harvest is a far more efficient use of space.
Start the seeds and veg for 18 hours a day in the small tent. The 4x4 can be for flower only. 12 hours a day of light and it can not have light leaks on it when it is in darkness. Very important to be in total darkness.
I guess if I had the option, I'd build low power COBs into the shelves.
About 80 watts of CFL per level or 10 watts per square foot would be a good place to start. Swap for lower watt bulbs if it's too hot.
A couple of 6500k cfl bulbs can handle a small veg. I assume you're putting the 120 inside of the 4x4? Make sure you have zero light leaks. I'd keep the 120 outside of the 4x4 if possible.
Also, Mars lights aren't exactly top notch...
I modified my Mars light into true COBs and it was a huge...
I'm a stoner, I grew leaf lettuce not head lettuce, forgot why I was doing it and we have been eating salads all summer.
Well, I should probably try again. What are we shooting for here?