Open source and FOSS are two different things though. I think Mattermost is open source, just not FOSS and the licencing they mentioned might be wrong (GPL is invasive so they couldn’t have a closed source part IIRC), but it’s still open source as the code is freely available.
That’s a very cool idea, seems great for receipts and quick stuff.
If you’re going to use Arch you should use Arch. One of the biggest advantages for Arch is the AUR which can cause many issues on Arch based distros that are not Arch.
That being said, for a media center, if you’re not used to, I wouldn’t go with Arch, Debian is a much better choice since you’re already used to it and should be good for that use case.
Sure, but which OSD criteria is being broken here?