2 of my 4x 4TB spinning drives are portable. 2 in mirrored raid, and on-site backup, and an off-site backup. If you don't have it on 3 drives across two sites, you don't have it. 5400RPM is fine as long as you allocate some of that NVMe as a cache for it. Keep all high-transaction stuff like databases, thumbnail caches and indexes on the NVMe drive. Going to 7200RPM just increases power consumption and noise, and reduces reliability.

The other specs seems fine, but I personally upgrade my desktop then take the old CPU, RAM and motherboard to use for my server.

Immich and Nextcloud run fine on my 2015 Core i5 with 16GB RAM.