Oh! Also, try posting this here: https://practicalzfs.com/. That’s a discourse forum really focused on ZFS. Jim Salter runs it and Alan Jude often contributes advice. There are some folks there who know ZFS inside and out.

Checksum errors can often mean a failing component. It could be the other drive or maybe a sata cable. Is the original pool mounting correctly? If so, you should be able to do a simple rsync to move it to the new pool.

I don’t think there’s a right answer for most of these, but here are my thoughts.

Data: I almost always prefer bind mounts. I find them easier to manage for data that I’ll need to deal with (e.g. with backups). Docker volumes make a lot of sense to me when you start dealing with multiple nodes and central management, where you want to move containers between nodes (like a swarm).

Cache: streaming video isn’t super latency sensitive, so I can’t think of a need for this type of caching. With multiple users hitting the web interface all the time it might help, but I think I’d do that caching in my reverse proxy instead.

User: I don’t use the *arr stack, but I’d imagine that suite of applications and Jellyfin all need to handle the same files, so I’d be inclined to use the same user (or at least group) on all of them.

DLNA: this is a feature I don’t make much use of, but it allows for Jellyfin to serve media to devices that don’t run a Jellyfin client. It’s an open standard for media sharing among local devices. I don’t think I would jump through any hoops for it unless you have a use, but the default setup won’t get in your way.

Hope that helps a little.