That idle power consumption doesn’t seem right. That’s less than a Raspberry Pi.

One of the better free options is FreeDNS, but you are limited to 5 records.

If you want your own domain, I would suggest Porkbun. They have an API that can be used for dynamic DNS.

You can use stunnel to make your VPN look like HTTPS.

Most ISPs have remote access to their modems. You should use your own if possible. If you can’t, then put it in bridge mode and connect your own router to it.

OPNsense doesn’t officially support ARM. You need an x86 PC for it unless you want to mess with an experimental build.

OpenWRT does support the Raspberry Pi though. You will want the Pi 5 for that since it has PCIe to connect an ethernet card to.

Backblaze personal doesn’t support Linux or BSD, so it would be useless for a NAS.

Just make sure you’re not using an EUI64 address. That significantly narrows down the number of addresses per subnet to scan. The bots found one of my computers that was using one. It took them 3 years to find it though.

The only thing they are good at doing is producing loads of RFI and pissing off every ham radio operator in the area.

Be sure to keep everything up to date too. Even openssh has had multiple vulnerabilities just this year.