Hi, monitor nerd here. The two key things I keep an eye on when it comes to monitors, are to get as many full-size (1080p or "1200p") working spaces as possible, and to retain a pixel pitch (will abbreviate "pp", aka dot pitch) within roughly 0,25 to 0,27 mm. That's the pixel "size" at which I find text easy to read and UI elements easy to use, at the viewing distance I personally like to have to my monitor. It means I don't have to rely on/fiddle with the UI scaling in each OS/VM, I get no mid-pixel text AA problems, and I'm only paying for pixels that I can use and see.
As a result of this, I personally wouldn't buy a 4k monitor/TV that is smaller than 43 inches. Which is huge! And awesome, because 4k at a usable pp gets you four full-size working spaces. I can highly recommend a 43-inch monitor with 4k resolution (pp ~ 0,25 mm). It boosts productivity in a great way.
There are a new set of formats called ultra-wide, or UW. The idea is to have two full-size working spaces side-by-side in one monitor (or three narrow ones), which would be a good option too for multitasking without looking at black monitor edges. Starting with 1440p UW, I could recommend this in a 38-inch monitor if you want loads of vertical space, but there are no such products available. As for the next step down (1200p UW), this would be great but there are no products available in this category. Lastly, as for 1080p UW, I would choose two 1920x1200 displays instead to get more vertical working space.
The next step down in monitor size, while retaining my personal favourite pp, would be one of the 1440p monitors at 31,5 or 32 inches (pp ~0,27/ mm). This is a good choice if it's important with loads of vertical space, but I wouldn't expect to be able to put 720 pixels x 2 to good practical use - i.e. this wouldn't give me four usable working spaces. I know however that a lot of people like to use this screen setup with three working spaces (one large, one tall and one wide). However, for many creative tasks, a good amount of vertical space is crucial.
As for multi-monitor solutions, a popular and sensible choice (to me) is X number of 24-inch monitors at 1920x1200 (pp ~0,27 mm). With monitor arms, this can work with anything from one to six monitors (two rows of three) which can be good from a future-proof perspective. Buy one, upgrade with another on your birthday, buy a third on Black Friday, a fourth when you're sad-shopping, a fifth when happy-shopping and the last one while really drunk. Just an example.
I'd like to point out that these are my personal preferences, and roughly estimated. For instance, I could probably go with a 40" 4k monitor if I just sat a little closer. But I've actually tried this and didn't like it. I also want to point out that if you have no problems with the OS UI scaling or if you like the 0,23 mm pp more, then the above advice can be adjusted to a warm recommendation of the 34-inch 1400p UW monitors. They are great for you. But I do recommend getting terminal glasses if you're not scaling text and read on a 0,23 mm pp monitor! Additionally, if you also would like to spend some money on really smooth text, I would recommend 2X products such as 4k on 24-inch monitors as they are... really smooth. Just keep in mind that it will cost you more, require a more powerful computer and limit you in terms of the number of monitors you can setup. Note that 27" and 5k makes no sense to me, I would go with 32 inches for 5k, as it's 2X to ~0,27 mm. But again, if you like the 0,23 mm pp more, then go for it!