Personally, I’d go down the route of getting a NAS, either a commercial off-the-shelf unit or build you own with something like an HP MicroServer. The Gen8 Microserver is getting a bit old now, but for NAS duties it would be perfectly fine you should be able to pick it up for a reasonable price secondhand.

The fact Pi prices have been so high is what has driven everyone down the mini pc route. Cheaper, more expandable and more performant.

Get the riser and a PCIE card. Riser gives you more flexibility long term.