Depends on the card. Also depends on how many frames-per-second you're going for. A 60Hz refresh rate for four monitors is definitely doable with the right card, which works great for a work/productivity setup.
If you wanted something like 120hz or 144hz with four 4k monitors, you'd probably have a harder time finding a card that can push that many pixels at that refresh rate.
And yeah getting the right window/monitor setup is a whole process. Alt+F7 (at least on Linux) works to grab/move windows that get bumped off the screen.