Questions about QNAP TR-004 Expansion Unit

Does anyone have experience with 4x12 TB hard drives or what is the maximum?

How many of the extensions can I connect to my Qnap 453D? Is only one extension possible or even two on one NAS?

Suppose I have created a Raid 5 with four hard drives and want to increase the storage later? Can I use four larger hard disks without further ado as with a normal nas or do I have to set up a completely new nas and the data will be deleted?

Is it possible to connect it to any qnap nas? The problem is that my hard drives are full and I'm looking for a cheap way to expand them? Always no cheaper than using 4 new hard drives Is that possible?

Is it possible to configure a RAID on the TR-004 when using it only as a DAS or does it have to be connected to a full NAS? I am looking for a DAS with which I can configure 4-6 hard drives as RAID5. I don't need any network features, just archive storage with failover. My search has been rather difficult so far.

What is the item number for the replacement power supply unit?

if you create a raid 5 with only 3 disks, you are stuck with that, you cannot add a fourth without wiping out all the data. you must start with 4 disks if you want to have a fourth disk.

I have a Qnap ts-451 in Raid 5. Can I extend my existing Raid 5 with this extension? Or do I then have 2 Raid systems? I use the NAS as storage for my Plex server.

Is the USB 3.1 Gen.2 up to 10 gps Type C -> Type A cable included?