I use a 40" 4K monitor and a 24" 1200p monitor, since it is my main desk.
The 40" monitor is fantastic, but for music you'll need a deep and wide desk to have the speakers on each side. For many people, 27"-29" will probably be a better fit.
I've worked for many many years with 2 monitors. It is ideal in my opinion, 3 or more is very problematic for music unless you have the space.