This is likely a general support issue. most likely split level related, please start a thread on the general support forum, enable mover logging, run the mover and then download the diagnostics and attached them to your post.
It should be fine to remove as long as "power supply idle control" is correctly set in the BIOS, see here:
https://forums.unraid.net/topic/46802-faq-for-unraid-v6/?do=findComment&comment=819173
This is only for when the cache if fully allocated but there's still free space, your pool is completely full so you need to move or delete some files.
If the VMs are Windows this helps to keep the vdisks as small as possible.
No.
You can use the default RAID1 profile but only 256GB total will be usable (and be aware that the free space shown on the GUI will be wrong) or create a single profile pool where full space will be available but without redundancy.
They'll turn green as soon as the parity sync finishes, independent of the disks being formatted or not, though you need to format them before use, and that can be done at any time, before or after the sync finishes.
It should work fine but make sure you confirm by checking if the emulated disk mounts correctly before rebuilding on top, more details on the procedure here:
That suggests fs corruption, see if you can get the diags on the console by typing "diagnostics", then type "reboot" and if it doesn't do it after 5 minutes you'll need to force it.
This one should work in any board but it's for SATA m.2 devices, not NVMe
This one is for NVMe and it should work in a x16 slot that supports PCIe bifurcation, check board manual.
The problem is the way the RAID controller is identifying the devices:
Unraid considers that those 3 devices have the same serial number so you can only use one of them, see if that identifier can be changed or better yet don't use a RAID controller.
By default only 20% free RAM is used for write cache, after that you're limited by the device, you're also a little limited by network and/or shfs as initial speed should be closer to 1GB/s.