Check wat was left on cache, mover might not move everything for various reasons, enabling the mover logger and running the mover will usually show the reason.
If the container is mapped to /mnt/user it won't be a problem, if it's using /mnt/cache you need to adjust.
It shouldn't make any difference.
It will only work for the first array start if the array is also set to autostart.
You can make a btrfs pool with both devices by adding them to an Unraid pool and then UD will mount it, you can also have and automatic rsync script run on mount.
Wouldn't worry about those errors for now, likely harmless, as for the temp warnings you can adjust the temps for that device, SSDs can run hotter, especially during prolonged writes, mas temp is usually around 70C.
You are having multiple apps crashing and btrfs is detecting data corruption there's also this:
BTRFS error (device dm-3): block=3573797388288 write time tree block corruption detected
Which usually means bad RAM, or other kernel memory corruption, start by running memtest.
As you prefer, for some time now that macvaln can crash the server for some users, it usually happens every few days, and macvlan related call traces are usually logged before the server crashes, if you have no problems you can keep using it.
Boot using the GUI mode and change the docker network to macvlan, apply, reboot and see if that makes a difference, if it doesn't you can easily downgrade back to v6.11.3 by going to Tools -> Update OS -> Restore