"Retro" consoles with thermal paste and system batteries...

I'd add watch out for dead caps and oxidation, but that's not my thing, I'm prolly missing tons of generic things and any device-specific steps.

I haven't done any myself, but I've seen people discuss common issues in videos about upgrading a retro console (ex. Fixing known issues and ticking time bombs before spending the money to upgrade the device with bigger storage or better ports)

Otherwise see if there are popular guides on ifixit: https://www.ifixit.com/

i usually don't do anything unless it breaks. (other than cleaning exterior dust)

plastic clips on those consoles are fragile, so frequent disassembly may actually have adverse effects

I've done nothing to mine and have no reason to not expect them to work if I unpacked them and plugged them in.