+1 on gas tanks (CO2 and beer gas) being outside of the keezer if you can. Made my 2nd keezer (upstairs) that way, and am so happy. Now converting my 1st keezer (downstairs); it's almost claustrophobic having the tanks in the freezer (esp. if you also run beer gas) and more work to do almost everything inside.
Since your CO2 tank(s) are now outside, you can use a 20# tank, which I much prefer to 5 or 10# tanks and is more affordable in the long run (refills). You can also easily sit the tank on a scale to monitor your volume, since a pressure gauge is ineffective for this purpose for CO2. I use this one with a phone charger-type power supply (instead of batteries) so that you can just leave it on if you like:
I use two 5" (120mm) computer fans; the one on the hump end is fitted to the underside of the freezer lid and hinged to be able to move it up and out of the way if needed. The second one sits at the freezer bottom on the other end. Huge improvement in temperature gradient management. As a time saver, I found these simple wire connectors for splicing and tee-ing your power supply lines to your fans. In Keezer #1 I did all my wiring with stripping, soldering, heat shrink wrapping, etc. TIME CONSUMING AND NOT NEEDED. These are cheap and kinda like the Duotight of small electrical wiring:
Definitely use something on the floor to protect the rather fragile freezer bottom from dings when moving kegs. I use a sheet of acrylic/plexiglass. Better than wood for beer spills, which can develop mold.
I use 3-1/8" shanks through my 2x6 collars; much better than 4" ones which can get in the way of moving kegs. (But I will put my taps on the hump side if there is a next time, which would also minimize shank/keg issues). I don't understand the comment against the 3" shanks; they definitely do work in 2' thick collars. Also, use stainless steel shanks and ones with 3/16 ID, if possible.
I use an Inkbird temp controller, with the probe placed in a small water bottle with about 15% or so of glycol in it. I place the bottle on the hump and on a piece of insulation so that its temp is not overly influenced by the temp of the surface upon which it sits, which may fluctuate due to the compressor going on and off.
+1 on Duotight connectors/EvaBarrier tubing. Use RO-style plastic locking clips on all push connections. I also use gas teflon tape on screw connections, especially any MFL connectors which do not have nylon tips (I also use nylon flare washers on those). They say you don't need these, but my experience shows that I did, and it cannot hurt.
I strongly recommend the use of Intertap springs for your faucets, and am amazed it took me so long to discover them. They work in Perlick forward sealing faucets (which I also recommend). They don't work in flow control faucets, but ball lock poppet springs do work (two "interwoven" springs per faucet is plenty of force to return the tap handle).
I labelled the top of my (black) lid with "Chalk Ink" pens for both the taps and the kegs. I use their water-based pens for items like labels and info that will change (easily wiped clear with water). The more permanent items like boxes and circles I used their "pro" pens, which do not come off except with acetate (but easily comes off if needed). MUCH better than real chalk! I built the one below originally as a conditioning keezer for 6 kegs but then decided what the heck let's add some gas and taps, but I only needed 4 serving taps. The keezer downtairs has 6 taps, which together with the 4 is plenty, since I will always have a few empty slots or duplicate kegs which do not need taps.
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And use plenty of silicone sealant on all joints and places where outside air could enter the keezer.
Good luck!