For frequently changing data hourly up to 24, daily up to 7, weekly upto 4, monthly up to 12.

For daily changing data daily up to 7 and etc. as above.

For seldom changing data a backup every 3 days with rotation based on a storage quota, and retention of manually held samples.

Did you read it to the end?

Without root user login, the attacker would have to guess not only the password to the user but also the username (hopefully it’s not something simple like admin), and once you are logged in you can use sudo -i to chage into root, which will require a password, therefore, we also disable password login so if someone does manage to somehow compromise the SSH user, they’d still need the password to become root.

Either use a dynamic DNS service, as many others have mentioned and probably easiest, or, assuming you only want yourself to have access to the services, another option is to use something like Tailscale or a WireGuard/FRP instance in a static VPS as the rendezvous point.

I was flat out rejected by my ISP to have a static IP, though I only had it changed once since I started hosting services, so ahatever.

Never expose the bare remote control endpoint publicly. For example, recently macOS had a critical vulnerability where an attacker could completely bypass authentication on their Screen Sharing daemon, and the researcher had estimates around 40k publicly exposed systems, and it was found out that the vulnerability was in fact being used in the wild. Exposing things like that publicly is asking for trouble.

Personally I don’t like relying on 3rd party systems like Tailscale, so I just have a WireGuard peer running firewalled to only allow access to what is necessary, though you can skip the firewall part. This obviously assumes you have a routable public IP, i.e. no CGNAT, if that’s not the case Tailscale is probably what you want.

The way a reverse proxy works is to literally stand in the middle of a connection, so either side only sees them communicating with the proxy, oblivious to the actual endpoint. The only “solution” to this, though it’s more of a hack really, is to somehow send the original IP as additional data in a way that both sides agree on, e.g. the X-Forwarded-For header as others have mentioned, however, as I’ve said, both sides need to support and aggree with that, so you may have to find a setting/config to enable on the services behind the proxy. Think of it this way, if services blindly trusted that header and you weren’t using a reverse proxy, a bad actor could send a request to your service with that header included thereby spoofing their identity in your logs, therefore, this kind of thing is usually opt-in