

FWIW, I bought a new Ender3 as a kit not too long ago, it was $150 IIRC. And by being forced to assemble it, I learned a good bit too. It might be worthwhile to watch their store & see if they put it up for sale again.
The only upgrade I’ve done that I really felt made a difference was buying an enclosure for it. Nothing fancy, it’s a fireproof bag over an aluminum frame. Even more than controlling the temperature, it also keeps it dust free when not in use - that’s probably the biggest win for me.
As for buying the used one - these things do wear down. Start by checking the feed gear & the PTFE tube. If the filament feeds well, then also check the belts, rollers, & nozzle. Those are really the common wear items imo. Perhaps obvious, but make sure the seller gives you a copy of the slicing software (should be free on their webpage) and also the little USB-A to Sim card doo-hickey that you need to move files back & forth.
So, I’m a novice Linux user and have been on Ubuntu for maybe 2 years now. And I’m just starting to really hit the SNAPS wall - IE, just a bit too much of what I want doesn’t install through snaps. Is there a good progression for my “next distro after Ubuntu?”. Still need some training wheels, but ready to take the next step.