I’ve got this up and running on my server. It works pretty well at the moment.
It seemed a bit wonky when I first set it up - I had to submit the form for a new account probably a dozen times before it went through, and clicking on links was generally hit or miss. Adding the Mattermost hostname as a server alias under DNS seems to have fixed this issue.
For TLS, I have edited the settings on the Virtual Host to use the correct certificate, and kept the the Mattermost TLS off. I tried using the Mattermost settings, but it doesn’t seem to play well with the Virtual Host.