Caching with nginx & multiple ghost instances on a single ghost

I’ve got 3 ghost instances running on a single digital ocean host. Everything is generally fine, but I love to tweak to make things even better. I’m running Ubuntu 20.10 and nginx. Now I’m looking at adding some caching to make things even speedier. I found this guide and had a couple questions…

First, is everything here still relevant for 4.0? Is there a better guide for this that I’m not finding online?

Second, when it comes to caching theme assets, you have to edit the sites-available/ghost.conf every time that you change a theme. Is there a better way to do this that I’m not finding?