Hey, y'all!
I decided to write a blog post and explain how to run Mastodon using Arch Linux. It's the same routine I use for https://masto.donte.com.br and https://lewd.town so it's fairly battle tested!
Here's the post: https://lond.com.br/2018/07/13/running-a-mastodon-instance-using-archlinux.html
I did test the guide by creating another instance, but if you have troubles or questions, ask away!