I would recommend my own current screen setup, which is 1 30" (2560x1600) in the middle and 2 24" (1920x1080) on the sides.
My arrangement window is always on the large screen which really makes a difference because of it’s higher resolution. It’s amazing how much more tracks can fit on screen without having to zoom out, making everything smaller and losing detail of MIDI notes and audio waves on your parts.
Then I have one mixer on the right screen (instruments, midi and audio tracks) and another on the left screen (send fx, group channels, busses) The difference in resolution of the screens is not annoying in any way, though you might want to consider having 2 27" (2560x1600) on the sides instead of the 24" (1920x1080) ones. This didn’t fit in my studio however, because the larger size of the side screens would get in the way of my speakers, which are behind that.
In short, a higher resolution is great for your arrangement window, however having multiple screens to view arrangement + mixer simultaneously is a must and in my opinion you can’t do this on one 30" (2560x1600) screen. I tried getting the arrangement and mixer all on the middle screen but it’s just too cluttered together and dividing this over two screens is much better.
So if you have to choose and can’t do both I’d say multiple screens is better, preferable three, so you have one in the middle. The gaps between the screens won’t matter then. They’re only annoying if you have two screens and the gap is right in front of you. I even have some space between my center screen and the side screens.
Hope this helps.