Been using Mint 18.3 on my Plex/media server for about 2 years. No complaints, except for two small ones.

1) The file manager (Nemo), has a tendency to crash when creating folders. I opened a bug report and got a solution that helped but it still happens enough to be slightly annoying.

2) I mainly use Plex but also use Emby for some things and in Mint, there is a NASTY memory hole of some sort and after a few hours, Emby eats up practically all available RAM. I brought up the problem on Emby's forums and nobody really seems to be able to fix it. With Antergos, I don't have this problem.

3) Seeing as how Mint 19 was recently released, I know I'll still get security updates for 2 more years with Mint 18.3 but after that, I'll have to move to 19 so I can continue getting updates and security fixes. Since Mint upgrades to whole versions isn't recommended, reloading my server every 3-5 years isn't a thought that thrills me. This is why I like the idea of a rolling distro.

I really think that Antergos is the Arch based distro that I'll end up going with. Is anyone running their Plex server on Antergos? If so, how long and have you had any problems with updates breaking things?

My hardware isn't too exotic. i7 7700K 4.2Ghz CPU, 8 gigs of RAM, Gigabyte Z170X-UD5 motherboard and an LSI 9207-8i v19 HBA with 18 drives attached to it (MDADM RAID 6), using built in Intel GPU.

Think I'll be OK?

You could try Debian. You only need to upgrade every 5 years. And if you specify a branch, i.e. stable, testing, in your sources.list, rather than a version, i.e. stretch, you never need to upgrade. You'll just keep rolling with that branch.