Hi! After many years I finally pulled the trigger and am ditching google photos and going self hosting.
My main goal is to provide a safe archive for all my family photos, digitized VHSes, etc (around 2TB at the time, expected to grow, but not super rapidly). Since we are talking about literal tens of years of memories, I really want to do this properly, hence I ask for approval or hints what to improve. I obviously have a somewhat limited budget, and want to go as low on energy as possible.

What I'm currently setting up:

Main machine (Celsius w550):

This guys has like ~20-25W idle power draw. I can put maybe even 6x 3.5inch HDD without much hussle and the drives are ventilated very well.

Specs:

• Xeon e3-1220v5
• 16gb unregistered ECC ram
• Some random APC UPs that has not arrived yet
• GT 710 because I need video output and maybe for some simple transcoding

Drives:

• "Important drives": 2x 4tb exos 7e8 in RAID 1 for critical stuff (bought them almost new with <30h powered-on-time. They have "DELL EMC ENTERPRICE CLASS" sticker)
• "Unimportant drives": 1x 4tb exos 7e8 (same as above) without RAID for non-critical stuff, if I decide to, e.g. run Jellyfin.
• 16GB Intel Optane M10 as boot drive

Off-site backup machine (Hp Elitedesk 800 G1)

This guys has like ~15W idle power draw, but only 1x 3.5inch HDD bay without any mods.

Specs:

• Some 4th gen i5
• 8gb NON-ECC ram
• No UPS

Drives:

• 1x 4tb exos 7e8 (same as above) without RAID for syncing with "Important drives"
• Random sata ssd for boot drive.

The plan:

• Install truenas scale on both machines.
• Install immich on Main machine and store all my photos and videos on "Important drives"
• Sync contents of "Important drives" to my Off-site backup machine every week or so, using snapshots.
• Since off-site machine has no UPS, no ECC, no RAID I think I want to figure out a way to verify that contents of files on that machine and main machine match, every month or so.
• Don't bother syncing contents of "Unmportant drives", they are not very important.
• Setup the systems, so that the drives spin down to make them quieter and draw less power.

Questions:

• Is no RAID on off-site machine a horrible idea?
• Is verifying contents of off-site backup and main machine a common/good practice?
• 3-2-1 says two types of storage. I only have one. Should I care? If so, what do you recommend?
• Immich is sort of experimental from what I understand. Should I avoid it for my important photos?
• Does this setup even make sense? Any other hints?

Thanks in advance for your help, I really don't want to screw this up.