NX500 still worth it in 2020?

Hi and welcome to the forum

Things to look for:

1. Faulty mode dial - by far the biggest problem with NX cameras. If you don't need to change modes quickly and you are willing to hack your camera, I made a small tool that will kill the mode dial and reassign that function to another key combo. Mods also enable silent shutter (at the price of reduced DR - essentially more noise in shadows) and various video things, more configurable time lapse, focus stacking, etc. Might not matter at all to your use.
2. The SD card tool (available at github repo for nx500 modding) will show you the shutter count, etc, which can be useful information.
3. Dead or stuck pixels - nothing specific to Samsung, most cameras show some in time, are visible in higher ISO / longer exposures (like 4s low light). Can be mitigated by subtraction of dark frame (automatically triggers for exposures over 4s). Not visible in general use.
4. Battery - if it's not original or you have any issue removing it from the camera - throw it away and get a charger and a pair of batteries (Wasabi have been good to me) for under 20 USD. If you have to keep the battery and it is not easy to remove - stick a tab (folded sticky tape or similar) on the side that enabkes you to pull it out.

Regarding lenses:

1. 30mm - also my favorite. Slow to focus but fantastic otherwise. If I ever sell my NX gear, I'm keeping it and a body.
2. 45mm - great image quality, fastest prime to focus, 3D is a gimmick, but can be fun for miniatures.
3. 16-50 could be the best kit lens I had, but, being a kit lens guarantees not guarantees on sample variation. YMMV. Surprisingly decent macro abilities but you're buying 60mm so not that important.
4. 10mm - bought it for 360 panoramas, ended up using it for fun Ridiculously small and fun. Did I say it's fun? Not for every day, though.