If the data on the emulated drive isn't available possibly there's a filesystem problem, and rebuilding won't help, if you still need help please post the diagnostics: Tools -> Diagnostics
Memtest isn't 100% reliable finding errors, only when if does find some you can be sure there are problems, not finding doesn't mean you can rule out bad RAM.
Very unlikely the SSD is the problem for this, also don't forget you have corruption on the array disks, first candidate would be RAM, followed by the board or controller.
Disk9 needs a filesystem check, but that's likely a result of the previous crashes, not what caused them, since the syslog doesn't survive a reboot best bet to catch the reason why it's crashing (if it's not a hardware issue) is by enabling the syslog server/mirror.
Just do a regular copy, you can use for example midnight commander (mc on the console), not sure all data will be available since it was a raid0 pool, copy what you can.
That's normal, parity swap procedure needs to be done from start to finish without any assignment changes, if there are any after the copy (or a reboot) it will be reset and you need to start over.
That doesn't make much sense, if a file starts writing to cache it will finish writing to cache, or give an error, it can't change to the array mid-write, it can if there are several files.