Monitor refresh rate just means how many frames or cycles it can display per second. 60Hz can show you 60 frames per second or 60 'cycles per second' (Hertz = cycles per second)
Unless your setup can push a steady 144FPS in your favorite games, it's unlikely that you'll notice much difference, other than a LOT more screen tearing as the framerates jump about.
As biker said, 99% of recorded content is 24-30 fps, and thus would display exactly the same on a 60Hz panel as on a 144Hz panel. Your positive experience with your 144Hz panel is probably more to do with it's colour clarity or pixel density, not the refresh rate. At best, SOME youtubers now upload vids in 60fps, but very few
whether or not you can run two 144Hz panels together depends on their resolutions. If they are all 1080p panels, then yes; no problem. The more pixels there are on the verticle axis, the tougher your GPU has to work to render and display images to you. You can mix and match whatever monitors you like, as long as:-
A) you have the video outputs to do it
B) you aren't trying to use NVsurround or AMD EyeFinity
If you wanted to run surround ideally you want to have three identical panels.
If you want the best possible viewing experience for watching content, and aren't too fussed about gaming; get a nice quality IPS display capable of 60-75Hz refresh rates. 75Hz is the sweet spot, IPS provides superior colour depth and clarity. Ideally, you'd want it to be 1440p as opposed to 1080p as well. 4k is still a bit of a gimmick at this time.