Get a hold of the schematics for your fridge if you plan on cutting through the wall to ensure that you do not hit any wiring or fluid lines.
A combined temperature and humidity controller like this one from Auber or this one from Inkbird would help reduce clutter, if only by cutting your controller units and accompanying wiring down from 2 to 1.
The complexity, consistency and reliability of your humidity control is going to depend on a lot of things (the fridge design, ambient temp and humidity, how much space you can fill up in the fridge). IMO the most maintenance-free humidity control is a large salt saturation reservoir. While under ideal situations the highest it can maintain is 75% RH, situations are usually not ideal and the level drops down when the compressor runs. But the lower the ambient temperature, the closer you'll be to 75% (compressor runs less).
This unit from Sensorpush will give you the data logging you need. In a large fridge, you may consider two and move them around initially to find if you have any hot/cold spots, and also see how humidity changes around the interior.
Some sort of fans to increase airflow beyond what the fridge itself is designed for is helpful. I and others have used these from AC Infinity, and they can be daisy-chained together in case you need to cover a larger volume than two can handle. Cost effective, low profile, low energy draw and they've been dead reliable for me. Variable fan speed so you can drop down the CFM's towards the end of your aging and reduce excessive drying.
If reducing clutter is paramount, I don't think much else is absolutely necessary. But a UV-C sanitizing light like this one provides peace of mind, at least for me. It doesn't take up a lot of space, and is for the purposes of dry-aging is maintenance free as the only thing that will ever need replacing is the bulb and has a lifespan of 10-12 months.
Just like with a regular fridge, keeping the condensor coils on the back of the fridge clean improves their efficiency.
Make sure your door seals are in good condition with no cracks or deformations.
If placing the beef directly on wire racks, make sure the racks are coated in a food-safe and corrosion/humidity-resistant coating (no chrome).
S-hooks if you plan to hang your meat from racks instead.
Thoroughly disinfect both compartments of the fridge before initial use. I used a vinegar/water compound. Also disinfect any components that will go into the fridge before they go in.
Your setup and arrangement of components will likely change a few times when you first start out, but try to minimize the amount of changes you have to make by thoroughly planning it out as much as you can. Consider how you'll position the cuts (hanging? standing on end? Lying flat? Will the positioning allow enough airflow around the cuts? Will drippings fall on sensitive parts like probe/UV-C light/fans?), the available length of your various wires and how you will run and secure them, where you'll place your temp and humidity probes and sensors, the position and directions of your fan(s), can the wire racks even support the weight of two primal cuts (my typical rib primal is ~25lbs), etc.
There's not really a step by step since everyone's DIY will be different.
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