the sounds I was hearing were very random for a while, then I guess it got to the next level where it made more predictable sounds for some time, and then it entered a new phase which we'll call banshee howls.

To me that sounds like either brake pad shims, or the the caliper/rotor assembly. Might be the dust shield bent out of place as well. On previous vehicles, ive used thin cardboard around the edges of pads(backside) to silence them because the thin metal shims were bent or not uniform.

You said it all started after a caliper seizure, are there any bent or broken parts that you noticed? Outside of that, Im gonna put my money on the "anti-rattle clip" or "quiet-shim". IDK where you buy your car parts or how much you like to spend, but i see a high end euro kit, and top shelf weaver kit that includes the dreaded shims. If you have them on your pads, try to RTV them or insert a small pad (cardboard, gasket) between the shim and pad.

If one side is bent or not making contact properly, that would explain why its only in reverse. Good luck