Greenfield NAS running pure NVMe and SSD for Plex

I'm building a new home NAS (moving away from my trusted home Synology) for Plex, music and some docker containers to run local dev build stuff (nothing too taxing). My setup is:

- Core i5 13600k (using for transcoding)
- x2 4TB NVMe PCIe SSDs

- x1 8TB Sata SSD (limited by 2 NVMe slots on my mITX)

- 32GB DDR5

I'm new to unraid (I was going to use TrueNas but reading up on ZFS needing ECC memory, I switched to unraid instead), and any tips would be great (its a fresh machine I'm about to build today) and my questions are:

• Which file format is best for media on Unraid?
• I had intended on using the NVMe as the fast memory for everything, and the 8TB sata ssd as a in system backup device. I've deliberately not spoken about RAID as I suspect I'd then peg the performance of my NVMe devices by the sata SSD speeds. Does Unraid out the box support backing up drives or do you have any recommended apps / approaches.
• I've got 6TB of data on my current Synology; I could create a drive mount between this and my new NAS. My first thought is mount the drives, and then from the Synology device copy / paste across the network (cuts out the need for a middle machine, which slows everything down). Any tips on this would be appreciated (trying to go as fast as possible with minimal write errors as I'm not running ECC ram).
• Is there a way to run some kind of checksum on my copied files to check if any have corrupted during the transfer?
• Plex, Ive got a plex pass and I've been reading about separating out the plex cache from the content by drives (i.e. put the plex cache onto another drive from the content), should I do this or can I just put everything onto one of the 2 NVMe's or am I better to put the plex cache data onto the SATA SSD and leave the content on the NVMe drives?

Thanks in advance for any tips or advice.