A slower CPU sucks, but swapping sucks even more. Is the ram upgradeable? You can get 16gb ddr3 sticks of ram. Idk how much EOL/the ram pocalypse has affected their pricing though.

Immich needs RAM so opt for more RAM if possible. I'm using Yunohost on an old box and have 8GB and Immich uses about 4-5 with all advanced features off.

I would go for the Wyse 5070 as a server. More RAM is good and the CPUs while somewhat slower are more power efficient.

The 4/5th gen Intel CPUs are the last gen that is really quite poor in power efficiency when mostly idling. 6/7gen made huge improvements in that regard.

Upgrading the storage should be possible quite easily.

Try to get as much ram as you can within your budget.

Containers don't need VT/SVM (unless you're doing something weird like Kata Containers)

I would go with a refurbished Lenovo TinyPC with a quad/hexacore and some 16 GB RAM. These used to go for 200-300 EUR, but this might have changed recently. I run an AMD Fujitsu thin client as my opnsense firewall.

I know you didn't mention video but if you think you might want to host jellyfin in the future, make sure your CPU supports hardware decoding for modern formats.

For example, my lenovo mini pc with an i5-6500 has support for h265 but not h265 10bit or AV1, which makes playing those formats on some devices basically impossible without re-encoding the files.

Just throwing this in here as another thing to consider - instruction set. From a quick check (so I'm happy to be told I'm wrong) the Celeron & Pentium options don't support AVX. That means some stuff - and I'm giving a hard stare at MongoDB here, but there will be others - is not going to run, or at best you're going to be either stuck with old versions or recompiling yourself from source.

(I don't know if any of your apps require Mongo or AVX, but I was bitten by this in the past and it was one of the main reasons I eventually upgraded one of my small clusters.)

Always go with more ram. I can say that from experience.

I'm partial to fanless, but keep in mind my empire of dirt is almost entirely fanless so I'm just partial to it.