A "me too!" and very loud from from me about apple refurbished. I've purchased two iMacs refurb from Apple and they had been great.
The last one was a mid 2014 27" 5K iMac and it lasted me very well. I mainly got rid of it because I wanted to switch to a Laptop, and I'd been eyeing up M3 Macbook Pros (refurb of course), but knew the M4's were coming, so waited to pull the trigger on once of those (I'm not expecting to replace it for quite some time), plus as it was older I could not longer upgrade the OS, it was stuck on Big Sur and some of the apps I was using were requiring later OS versions to run, and I get why (I'm on a dev team so supporting as few OS versions as you can is good in my opinion). I did subsequently find out about OCLP (https://dortania.github.io/OpenCore-Legacy-Patcher/) which could have allowed me to keep the iMac for a bit longer, but it's my own fault for not researching enough!
Depending on budget, maybe the low end M4 mac mini might be possible for you. there seem to be quite a few video reviews around from music producing types who seem to think they are excellent value for money, bar the stupid price of internal storage, but you can get an external SSD with a decent capacity for less than it'd cost you to go for the stupidly expensive Apple tax on an internal boost (There are seemingly upgrades for internal storage for m4 mac mini's so that might be a solution, but it would void the warranty, so maybe not)
If it's to be a laptop, then M2 should be ok, or if you can push it, an M3.
Displays on the laptop are pretty good, plus yes, you can hook up an external display. think recent macbooks have HDMI on them, if not a USB-c which you could connect up to a monitor. I've got my macbook hooked up to a 27" ASUS monitor, it's not 4K, but for what I need it's great.