Here's what I do (I use Cubase): I have the main Project window on the top half, and I have the Piano Roll Editor on the lower half. If I want to see more of the Project window, I hit the Z button (for Zone), and the lower zone with the Piano Roll disappears. If I want to see the Mixer window, I hit X (for miX), and a floating Mix window pops up on the top half of my screen. Hit it again and it disappears, showing the Project window again. My hotkeys came from Logic, because I used that before jumping to Cubase. Having been frustrated with different setups for years, I can promise you that I am extremely happy with this setup.If I had a 43" monitor, I know I would just make the main editing window on the DAW bigger and I'd still end up with at least one additional monitor for plug-ins! Also the iMac is what it is—a very nice 27" 5K retina display, but I'm locked into it for obvious reasons.
And also, even though it's a 4K monitor, I have it scaled to a Goldilocks setting where I can see all the tracks, but they're not so small that I have to squint to read the names.