itimpi

There is a button to do this on the Main tab.

Chances are it is the way you have a docker container configured.

This

Splitting only the top level is what you want for the distribution you say you want.
 
I believe that the problem with your TV shows is that Krusader creates all the folders before it starts copying files into them.   Since cresting a folder takes almost no space they all get created on the first drive and then the Splut Level setting constrains the files to that drive.    If you copy the files back in smaller increments then you should get the files split across the drives.   You would also get it if you used a copy method that does not start by creating all the folders required. 

You can use the New Config tool to change the disk assignments to what you want, but you then need to rebuild parity to match the new assignments.

Two alternatives that have existed for ages are automated backups via the CA Backup/Restore plugin and manual backups by clicking on the drive on the Main tab and selecting the backup option.
 

What you describe is not a standard part of Unraid.   Mover makes the assumption that a file only exists in one place, and will not overwrite a file that already exists on the array when trying to move files off the cache.
 
some people have written custom scripts to what you describe.   They exploit the fact that if a file exists in 2 locations under Unraid then copies on pools take precedence over a copy on the array (and pools are used in alphabetical order).   However it is then up to the end-user to manage any corner cases or unexpected behaviour.

1.  Yes.   
2.  Very easy as long as you have the ports available to plug them into.   They do not all need to be the same size.
3.  Many people run their Unraid servers headless.   You may need a monitor/keyboard temporarily plugged in to support setting up the BIOS to boot off the flash drive unless the motherboard you select has IPMI support (which allows this to be done over the network).   The Unraid management GUI uses a web browser so that can run anywhere that supports a browser.

The process is covered here in the online documentations accessible via the ‘Manual’ link at the bottom of the GUI.

Yes - parity is only important after a drive fails to reconstruct its contents.
 

Yes.  
 
The key thing is to not have any data drive accidentally assigned as a parity drive as that will end up losing its contents.
 
if any share have includes/excludes for specific drives these will need to be checked (and if needed corrected). 
 

Not that I know off.
 
The way to handle this will be:
make sure you have notifications enabled so you can get an email if a drive fails set up secure remote access using either My Servers plugin or using WireGuard VPN built into Unraid.   That gives you the ability to monitor and control the server remotely.

There is also the ‘mc’ (Midnight Commander) command from a terminal window which is friendlier than using the command line

Level 2 would be correct for your example as you only want to allow the Ozark level to exist on multiple drives.    Note that there is a bug if you are running 6.10.0 rc2 where changes to share settings do not seem to take effect until you restart the array.
 
The change only applies to new files.   It would take Manual action to sort out any files that are already on the wrong disk.

Using the Parity Swap procedure the system does not start over-writing the contents of the old parity drive until it has successfully copied its contents to the new parity drive.  If for any reason you get a failure during this stage you still have the contents of the old parity drive intact for recovery purposes.  As long as the parity copy completes the new parity drive takes over the task of emulating the failed data drive while that rebuilds.

You have corruption on disk 4 so you need to run a file system check on that drive.  File system corruption often causes the tort of symptoms you are seeing.
 

The Parity Swap procedure is not appropriate for replacing a failed parity drive  You should just be able assign the replacement drive and start the array to rebuild parity.
 
The fact it appears to not be showing up to assign suggests an issue at the hardware level. You might want to carefully check power and SATA cabling to the drive.  Posting  your systems diagnostics zip file might also help with diagnosis. 
 
 

You can find the Parity Swap procedure which handles this scenario in the online documentations accessible via the ‘Manual’ link at the bottom of the GUI.

You cannot change the file system type without reformatting (which effectively wipes the current data).   The only way to achieve this is to first copy the data elsewhere before reformatting the drive and then (if wanted) copy it back.
 
Parity is maintained when you reformat so will not need rebuilding.
 

You do NOT have the files mirrored - they are simply different views of the same files.
 
Usef Shares provide an aggravated view of files within a top level folder on all array and pool drives. You might want to read the online documentations accessible via the ‘Manual’ link at the bottom of the GUI to find out more.

You can use the procedure documented here in the online documentation accessible via the ‘Manual’ link at the bottom of the HUI.

As far as I know there is no way to change the format keeping the data intact.
 
As to what format is most suitable that does not have a 4GB limit it will depend on what systems you want to move the drive between.    For example if it Windows and Unraid then NTFS is probably the most convenient to use.

No.  With 6.9.0 you can have multiple pools (with user specified names), and any of them can be set to cache a share.
 
Under settings -> Identification.
 
 

The easiest thing would be to edit the config/network.cfg file on the Unraid flash drive to change the static IP to one in the new range
 

du is known to often not give correct results on multi-drive btrfs format arrays.

It looks like you have been getting messages about drives resetting ever since the system was booted on 7th Jan.   I did not spot anything obviously wrong in the SMART reports for the drives, so these issues may well be related to the power/SATA connections to the drives.
 
I would suggest that you shutdown the server, carefully check all the power and SATA cabling is well seated, and then power up the server to and get new diagnostics.