On one side of the spectrum you have the likes of Synology: you pay premium for the software that does what it says in a nice compact enclosure. Good documentation, easy UI, potentially limiting flexibility.

On the other side, you can make a linux box and declare it a NAS. Run whatever storage you want with whatever filesystem. Any enclosure and form factor you can imagine. Infinitely scalable, but also you’re absolutely on your own in configuring and managing it.

I’d suggest figuring a budget first, and then figuring how much of a hands-on approach you want to have.