I've been suuuuper lazy troubleshooting this so it's been a few weeks, but I talked to WD support, they said to run a full extended S.M.A.R.T. test on the drive, it passed with no issues.
Reconnected it to my server using a different SATA cable on a different port on the motherboard, with a different power connector. It resilvered with no problems, and a zpool scrub returned no errors this time so hopefully I'm in the clear!
I have a script that runs once a week that does a scrub then sends the output of zpool status to a Discord channel. When this first started it had read errors (as mentioned in the post), then checksum errors two weeks later. With there being a couple different errors before troubleshooting, and now with no errors after a scrub I'm hoping this means everything's fine now.
Both. Currently she wants help deciding how long to stay in which places, and wants help picking and booking hotels. So she's trying to wait until I'm ready to plan, but I'm basically never ready to plan until it's right before the trip and I need to rush to make up for lost time.