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.