I’m curious why you’re not running your own CA since that seems to be a more seamless process than having to deal with ugly SSL errors for every website

It's not, it's another service to deploy, maintain, monitor, backup and troubleshoot. The ugly SSL warning only appears once, I check the certificate fingerprint and bypass the warning, from there it's smooth sailing. The certificate is pinned, so if it ever changes I would get a new warning and would know something shady is going on.

every time you rotate the certificate.

I don't really rotate these certs, they have a validity of several years.

I’m wondering about different the process is between running an ACME server and another daemon/process like certbot to pull certificates from it, vs writing an ansible playbook/simple shell script to automate the rotation of server certificates.

• Generating self-signed certs is ~40 lines of clean ansible [1], 2 lines of apache config, and one click to get through the self-signed cert warning, once.
• Obtaining Let's Encrypt certs is 2 lines of apache config with mod_md and the HTTP-01 challenge. But it requires a domain name in the public DNS, and port forwarding.
• Obtaining certs from a custom ACME CA is 3 lines of apache config (the extra line is to change the ACME endpoint) and a 100k LOC ACME server daemon running somewhere with its own bugs, documentation, deployment and upgrade management tooling, config quirks... and you still have to manage certs for this service. It may be worth it if you have a lot of clients who don't want to see the self-signed cert warning and/or worry about their private keys being compromised and thus needing to rotate the certs frequently (you still need to protect the CA key...)

likely never going to purchase Apple products since I recognise how much they lock down their device

hear hear

there are not that many android devices in the US with custom ROM support. With that said, I do plan to root all of my Android devices when KernelSU mature

I bought a cheap refurbished Samsung, installed LineageOS on it (Europe, but I don't see why it wouldn't work in the US?), without root - I don't really need root, it's a security liability, and I think the last time I tried Magisk it didn't work. The only downside is that I have to manually tap Update for F-Droid updates to run (fully unattended requires root).

I’m currently reading up on how to insert a root and client certificate into Android’s certificate store, but I think it’s definitely possible.

I did it on that LineageOS phone, using adb push, can't remember how exactly (did it require root? I don't know). It works but you get a permanent warning in your notifications telling you that The network might be monitored or something. But some apps would still ignore it.