I have two 27in iMacs on my desk; my older one and the new one I got last year. Before this I had the older 27in and even older 24in. It took a while to get used to two keyboards and two mice on the same desk, but now I’m fine and instinctively reach for the correct one.
The older one handles emails from all my email accounts (many) excluding my main work email. It also runs the music, my CCTV software and any other “background” stuff that I need to run 24/7.
Newer iMac is my main machine and almost always runs about half a dozen apps, each with their own desktop. Each desktop has only one app on it, although often more than one instance of it. I can’t work with more than one app per desktop, but got used to swiping between desktops no problem.
Connected to this newer iMac is a bog standard 24in Dell monitor; on this I run another email app with only my main work emails on it, a Finder window or two and normally an FPT client.
I split my emails between the two iMacs to help focus: I get notifications for emails on the newer machine but not the older, so I don’t get disturbed by any emails that land on it.