I need help with a new monitor for FCP, want 4k but I'm confused.

Okay, I am running three monitors now with my late 2013 Macbook Pro 15" top of the line retina. I want a 4k screen. However, only the 2014 and 2015 runs most 4k screens. Although there are some that are MST, which means multi stream transport, (I have no idea what that means,) that will work with my Macbook.

I can't seem to be able to identify which 4k screens I can use? I can use the other ones but it needs to be MST to be able to run at 60hz. I assume that is important?

It doesn't absolutely have to be 4k but I'm replacing an Apple Thunderbolt Display, I'd like it to be above that resolution. However, the only way I'd stay within that resolution is with the 21:9 ratio monitors.

Can someone recommend something that will work out of the box for me? I don't care if I have to buy cables. Do I need 60Hz if I don't play games? I mostly just use Lightroom, Final Cut Pro, Premiere Pro, and photoshop.