You can find cheap server chassis in my country for €100 for 2U/3U/4U with plenty of bays since it’s ultimately just a case. There’s plenty of space for any board in the case and you can get mount adapters for desktop boards to mount in server cases. Personally I’d build a bare metal Arch Linux host and run everything as Docker containers running on ZFS RAID-Z but TrueNAS etc is fine if you’re not familiar with building the host yourself. Arch has great documentation for every kind of service you’d want to run on the host.
As of right now, I live in a small studio, so noise is an important factor, forgot to mention that. I thought about server chassis but for them to be cheap enough, they will also be expensive and power hungry. So I was leaning more towards tower builds.