That's a great idea! In fact, I've been using my baseline Mac Mini M1 as a NAS host.

Here's my experience:

- Setting up File Sharing on macOS has a few tricks, but it works, and the speed is great, especially if your router supports Gigabit Ethernet.

- Setting up Plex for media server has been incredibly easy and satisfying. I installed the server app on macOS and then installed the client apps on my iPad and Apple TV 4K. The experience has been great.

- It's best to connect a DAS (Direct Attached Storage) with the USB-C cable so you can use multiple hard disks and set up redundancy and RAID.

- I managed to share an external HDD over a USB 3 port, and the speed has been suboptimal.

I heard the refurbished price of M1 Mac Minis went as low as $300.