toastboy

Unplug the fan. Fire it up and let it run for a bit. Take the side off (with the computer running) and check the temp of the heatsink. An IR thermometer is best, but even your finger is good. If you can't leave your finger on it because its too hot, it needs a fan. If you can leave your finger on it, its fine to leave the fan off

Can you not click that little triangle next to LAN2 and change it to LAN1?

I suspected it doesn't like the USB drive so is hanging trying to boot from it.

What happens if you delete your test file without un-linking? Does the file get deleted off your NAS? Try having multiple test files in your drive on only deleting one of them. I suspect the NAS thinks it has an empty folder so will copy everything over as there's no record in the drive of the locally-deleted file being removed.

I use Photo Station regularly without any problems. I've never done anything to make sure I have a valid serial number

You wont need the video card anymore so thats a help. However, the motherboard only has two SATA connections, so if you want to run more than 2 HDDs, you'll need an add-on card or replace the motherboard with something else. I have a NAS running an i3-4160 which is a touch faster, and its definitely capable of far more than I throw at it using Xpenology

Cloud station works just fine. Most packages work just fine Quickconnect runs through Synology's own servers. That's why its a violation.

Why not just set up two different volumes within DSM? Populate one with your RAIDed drives, and assign the other volume with non-RAID drive(s). I have roughly the same thing with my baremetal install.

I have one folder syncing to OneDrive, and I have two more folders each synced to a separate Google Drive account. Yes, 6.1.5

SHR is good if you have mismatched drive sizes. I have SHR enabled on mine because I have 2x3TB and 2x2TB drives, but when I eventually replace the 2TBs with the 3s that I have, I'll go to a RAID-5 If they're all the same, SHR is the same is RAID-5 (SHR-2 = RAID-6)

I use it in a small office setting and it works with no problems. I also have in synced to 2 different google drive accounts and all three work just fine. Do you have the sync schedule turn on? Does what's in the OneDrive cloud match whats on the NAS (more or less)?

Yes, VMM only works with BTRFS

Did you make the USB bootable? Thats a pretty important step. If you used Rufus, make sure to select NOT the UEFI option

Make sure it is set to boot off the USB (and is capable). You may have to hit the 'boot options' key or change a Bios setting or two. Some motherboards only want to boot from specific USB ports as well. Try one directly connected to the motherboard rather than a front-panel one

Have you tried doing it with complete fresh components. Fresh bootloader USB and without your old HDDs to see if that will do it? If you can get a working config, then plug in your old HDDs and migrate. I've had (and seen) issues where an existing DSM install on previous HDDs gets in the way of a new install.