1. Nvidia/Windows tends to not do well with 4 monitors, (this could apply specifically to 4 4k 144hz monitors). Had a bunch of reliability issues esp with returning from standby.    3 works great.  I've yet to try multiple gpus, I instead run two pc's.   If you care less about gaming I'd get the Nvidia a2000, It's basically a prebinned rtx 3060 with ecc, and lower power usage)  Likely would run 4 monitors at high framerates, but I have not tested it yet.  
2. Figure out if you are likely to notice a high framerate monitor, and if so get high framerate displays.  Your best bang for buck in 4k's (Assuming you care about latency and resolution and less about gaming or HDR) is the gigabyte m28u or m32. (28inch vs 32)  If you want smaller LG has a few, LGGN950 i believe.  Keep in mind heat output, 5 of these at 4k 144hz will draw about 200w of power.  
3. I'd get the 12900k or ks not the KF, so you get the added flexibility of the iGPU. KS is the prebinned intel OC'ed version of the K/KF.  
4. Your money is absolutely no object upgrade is an optane p5800x for your OS.  It's an enterprise drive with ridiculously low latency, makes your desktop usage much snappier.  I had a 905p previously, probably just as good in practice.
5. Quiet is all based on ambient temps and cooling.  Keep in mind modern processors do a great job of boosting their speed if they have thermal headroom.  Your best bang for buck option is to use an arctic liquid freezer ii AIO, as big as you are comfortable with.   High end is custom water cooling loops.  

(My current main desktop is a 12900ks, 128gb ram, 3090, p5800x.  previous was a 5950x)

Feel free to msg me if you want to discuss further.