I've recently installed WordOps for the first time on a new server and moved all of my (previously ee3) sites onto that server which is now my production box. These are commercial sites for which I can't afford downtime.

I'm currently here:

sudo wo --version
WordOps v3.9.7.1

I've made many customizations inside the /etc/nginx directory including changes to nginx.conf, the addition of an entire directory (custom/) filled with additional configuration files, and extensive modification of each of the vhost files for my sites.

I've also made extensive customizations inside /etc/fail2ban.

Everything is working well on this server, AND I'd like to try to stay up to date with WordOps updates if possible. At the moment, I'm afraid to do sudo wo update or even sudo wo update --preserve because I don't know exactly what will happen if I issue either of those commands. The documentation for the update process doesn't tell me anything about what will actually happen. So here are some questions:

If I use --preserve are there ANY files at all under /etc/nginx that may be overwritten?
If I use --preserve will new versions of the various nginx configuration files be written somewhere so that I could manually, safely incorporate any changes, or will I just not see those updated files at all?
What kind of updates happen outside of the /etc/nginx directory?
Will any files under /etc/fail2ban be updated or overwritten?
Do any wo stack services (phpfpm, mariadb, nginx, etc) get replaced and restarted during the update?
Is there anything that happens during the WO update that is likely to cause some period of downtime (and if so, how much)?
Is there anything that happens during the WO update that could conceivably bring all my sites down and leave them down until I manually make repairs to something that went wrong?

I really need this server to stay online. So I'm just trying to get a sense of how much pre-update testing I should be planning on. It would be expensive (time-wise) for me to set up an entire mirror of this beefy server as a test environment with all of my customizations. But maybe that's overkill and just a VM with one test site using my customizations would be adequate. I'd be able to get a better sense of that if there were some more documentation on what happens altogether during the update process.

If nobody has time to produce such documentation, maybe you could just post high-level development docs describing the update process along with links to the source files that do the updating so I knew where to look. I'm python-friendly.