Some words to my PC setup:
At the moment I use a Intel I7-11700, 32GB RAM, Big SSDs, RTX3070 and have the settings “4K/high or ultra” with resulting 25-35fps in 4K.
I have two monitors attached to the PC, the bigger one (32") at the RTX3070, the smaller is connected to the onboard grapics. Connecting both on the same graphic card can lower the frame rate in some cases. Especially for pop out instruments see here.
I use a second PC for Navigraph charts, Littlenavmap and Discord communication.
I plan to buy a 4K TV (45-50") for my main view.
At the moment MSFS does not support Multiple Screens Functionality (aka multi monitor) for the main view, whilst Pop-out is possible with some frame rate loss.
Multi-monitor is on the Asobo wishlist but I personally worry my graphic card will not handle 3 high-res monitors, so I focus on one big screen and extra screens or PCs for gauges or addon software.