Have you read the docs? I think that should give you the info that you are looking for. As noted there, you can preseed the inithooks and thus avoid the page you are highlighting.

Having said that, TurnKey includes a Let's Encrypt integration that relies on port 80 being publicly accessible. So if you want to use that, you'll need to allow port 80 (and ensure that you have a reverse proxy set up to make it publicly available).