Final Update
Firstly, once again, a big shout-out to the ASR community for lively and engaging conversation and helpful advice.
The Neumann KH120 II are still spectacular. I will not need a sub any time soon (when I hit 90dB, they literally circulate cool air in my small office and give me all the bass I need for now). I have not fiddled with any of the settings on the back of the speakers. I don't think I need to, but I do wonder if I should experiment anyway.
The WiiM Ultra does everything I want it to. It is spectacular. I don't foresee a needed upgrade path except if I wanted to go wild, buy a phono stage, pick up a Topping A70 Pro, and revert it to streamer-only duty - which I probably won't do because that would be buying stuff just for the sake of buying it. I can't foresee a necessary and valuable upgrade path, to be honest. I find myself constantly running room correction with various settings. I find that opening up the range to 30Hz - 20kHz gives me a more pleasant correction, even though the KH120s supposedly go 40Hz-19kHz. I worry that f***ing around with room correction will be where I kill most of my time, fiddling between B&K, Harman, and Flat curves, LS/HS settings at various frequencies, etc...and that I'll never actually listen to music.
The open-box Technics SL1210GR with Nagaoka MP-200 is sublime. It was used as a display only, and was never played, so it is literally brand new. For the price I paid (1.3K EUR with the cartridge included) I got the steal of the year, in my opinion. Limited vinyl collection for now, but Pink Floyd's Dark Side of The Moon, and Radiohead's entire discography play really nice. Subtle warmth with midrange precision, and while I can't quantify it, I feel like vinyl versions give me a wider sound-stage and instrumental separation than digital. Is that even possible, or am I being delusional?
Push-button on/off, electronic speed control...why I was even contemplating a belt-drive is beyond me. While I don't need the DJ features of the turntable, I am already messing with pitch to hear different versions of favorite songs. I love the detachable headshell option, because I can buy premounted cartridges if I ever chose to and not have to worry about the precision needed to mount cartridges on my own. I have set the stylus pressure at 1.5g which is the low end of the range suggested - I might experiment with 2.0g sometime in the future. No vibrations even with the Neumann right next to it, pounding hard. I attribute that more to the IsoAcoustic Mini Pucks I have for the speakers and the rock solid construction of the speakers themselves...although I am pleased I got slightly higher than an entry-level turntable with quality feet and heavy construction.
The only gripe I have, which is so wildly inconsequential that I am almost loathe to bring it up is that when my mini-refrigerator cycles, the sound drops out for the slightest bit of time. It's an old house, so it's likely that the fridge is on the same circuit as the speakers, but changing outlets hasn't helped at all. Curious if I need a UPS or some other (budget-friendly) solution. Recommendations welcome!
Thanks again, everybody!