timbosan:
Thought I would offer my take on the side by side question. I have 2 x 24" Dell 24" monitors, they are just over FHD at 1920 x 1200. I find having 2 separate monitors helps split areas of focus, whilst the resolution is just enough to have space for working productively on one monitor.
I do have a 25" 2560 x 1440 as well (not on my WFH setup), and ideally I would move to having 2 x 1440p monitors side by side, maybe at 27" as this would give the best combination of resolution, physical size, and pixel size.
Personally I don't see the advantage in 4K monitors if they are run at more than 100% scale, as it means you are not using the 4K resolution.
The other thing I am interested in is, what do people who use a single monitor, especially ultrawides and large 4k's use for window management?
I went from 2x 24" 1080P screens to the 27" 4K I have now and find that generally better.
The advantage of 4K even at >100% scaling is you get lots of UI elements that aren't tiny, but really good detail in them. It's not the same as just having a monitor with a lower resolution.
On Mac I use Better Touch Tool for window management (among other things). On Windows, I used to use DisplayFusion, but found the built in snapping in Win 10/11 to be fine.