I have a side by side setup. One side is always for lager fermenting / cold conditioning (being the freezer side). The fridge side has been modified to have a couple of fans in a push / pull configuration and lizard bulb heater. Each side has its own STC-1000 (actually the inkbirds, but same thing essentially), as well as a couple of override switches.
Override switches aren't needed, but handy every now and then. Plus bling factor. When I want to cold crash I can just ignore the STC and set the cool circuit (The fans between sections) and hit the switch. Constantly changing air between the two sides essentially makes one big chamber. Meanwhile the controller on the freezer side continues to do its own thing.
Should not need to state it, but the fridge side cannot be colder than the freezer side. Trying to do so would just have them reach equilibrium. Had it almost a year now and nothing has conked out yet.
Edit: Sounds as though you want to go with a keezer style switched outlet. I know these fridges have their own temperature regulation / baffle system to keep both sides at the desired temperature. I assume a switched outlet would have the fridge go into full chill mode every time the whole unit was energized. Now would it lose power via STC before the fridge was at real fridge temperatures? I can't say.
I went into the guts of my fridge and bypassed everything possible to make sure that it worked by my command, not something built in. In the back is where my compressor access was. Make sure to wire in the starting capacitor! In my model the compressor fan has a sensor with it, if it's needed or not. I hardwired it in to always run when the compressor is on for good measure. Either trace the wire to find the existing cooling fan or run your own (through the drain hole under cooling coils) and connect up that fan as well.
The push / pull setup for the other side is childs play by comparison. A couple of louvred duct fittings will help to prevent unwanted drafts.