I've been thinking about your design and I have a couple suggestions.

- I would put all intakes and exhausts at the back of the fridge. Otherwise the fridge will not be very stealthy with a bunch of vents in the sides.
- Put intake low and exhaust high, at opposite sides of the back, and a small, inexpensive computer-type fan at each opening. Perhaps just one blowing out might suffice in the bottom chamber.
- You'll want a bigger fan for the top exhaust, maybe 150-200 cfm.
- It would be pretty easy to mount the top fan on the outside, and a small carbon scrubber on the inside wall, basically attaching the two together. Your weed will smell very strong when it gets into flowering, maybe so strong people standing outside your garage could smell it. But you could always try a grow without a scrubber and see how bad the smell is, and mount it later if needed. There are also jars of gel that you can put in there that is supposed to work for smell, but I have my doubts how well they work compared to a scrubber.
- If you try the setup as mentioned and it gets too hot in the flower chamber, a quick fix is to mount or place a small fan on the center of your screen. Have it blow straight up at your light. This should solve any heat issues. You might want to just plan for it, because the light and fan combo as mentioned will likely be too hot. Also increasing the size of the exhaust fan and/or intake fans could solve the problem.
- Since the screen would make it difficult to move plants up and down, make sure you can move your light. There are professional-looking things to make this happen, or you can have all four of the chains you show hook onto a small nylon chord. It goes up and over a pulley and straight across the ceiling to the front right, over another pulley then down where you can easily reach it, and wrap it a few times around the tie-down hardware you put there.
- I'm not sure about the polystyrene sheet you mention for the shelf, but it needs to be completely opaque. I know light will shine through colored plexiglass, and this is not acceptable.
- Be sure to get some trays to set at the bottom of each chamber to catch run-off from watering, or you can just pour the water into the tray and they will soak it up.
- Otherwise everything looks good, and I think this can work. I hope you are still planning on making it happen.
- The things I say here are from years of experience, but I have been known to make mistakes from time to time. Please read other things and use your best judgment. In other words, don't come crying to me if something doesn't work out. Ultimately you are the one responsible for the results of your own actions.