So, I have the F4-423 and I found a guide on the F4-422 a while back.
So the way the system works, is there is a tiny flash drive plugged in, inside the case somewhere. You can replace it with your own, or flash over the existing one with unRAID. I chose to buy a new flash drive so it's a bit higher quality and takes full advantage of the USB3 port it's plugged into. I just swapped the flash drives and it boot into unRAID as it is already setup to boot from that flash drive.
For layout, I did 2 SSDs for cache and 4 HDD for storage. I setup the mover to move things off the cache to storage and things are written to cache first. Works fairly well.
Now, they might have changed things for the 424 but it is unlikely.
I also did the ram upgrade to 16gb while I was there
https://nascompares.com/guide/install-unraid-on-a-terramaster-nas-drive-a-step-by-step-guide/