I’m in the same kinda situation as you, I need some storage but need it to be expandable, want to run some docker stuff, while I could (and have in the past) build and maintain something like that from scratch, I don’t want it to take over my life and I want it to be easy to maintain. My previous NAS was fully set up from scratch on FreeBSD, it was pretty good but was a lot of work to get it right.
So I set up an Unraid server on a parts-bin server as a kinda compromise between a fully DIY and just buying a NAS. Meant I could use some old stuff I had and some cheap components rather than paying out hundreds for a NAS. Slapped in some shucked drives and some old NVMe drives (took the opportunity to upgrade my gaming machine, so used the old stuff for this), now got 42Tb of storage and 2Tb cache.
I have to say it’s bloody fantastic. Was a bit on the fence about a paid OS but it’s cheap, the UI is solid, and thus far totally worth the money.
Alongside about a dozen services running in containers, I’ve got an Arch VM to satiate my DIY cravings, which suits me fine because I can do what I want with that without messing up my file storage/services/etc.
Pi with Kodi on it is pretty good.