Most of my services are at home in a dedicated lan but I still have one vps server that is used as a reverse proxy and which forward everything via a tunnel.
The OS itself doesn't need much maintenance. I have set up auto updates and auto reboot on a regular basis. And you know what? Distros do their job very well and it just works. We are talking home service, I can deal with (less than) 5 minutes of downtime once in a week. I use rhel derivated distro which means major disruptive upgrade are only dealt with once every n years. I may choose an immutable distro in the future when support ends though.
Rotating https certs? Certbot makes automatic rotation easy.
ssh? What is the deal? You set it up basically once. Add a bit of port knocking if you want more silent logs.
To add a bit of security, set up crowdsec, fail2ban. Again, these tools do not require a lot of maintenance.
Most of the burden of maintenance comes from the management of the apps/services you want to have live. PaaS won't really help you much with that. SaaS tend to be expensive or lock you, they help if the service you want to maintain is complex. I don't think that is the case for the services described in the OP: static websites, git and backups.
There are traps though. For example should you run containers to easily maintain certain services or use the distro packages? You can argue that containers whom upstream project provide image for allows you to easily upgrade any service. I can switch from any postgresql version in a snap for instance. However while it is easy to track and set up auto update a major version using a tag, you might want to be more cautious with major versions bumps. And this keeping informed with the various upstream project, know when and why to do major upgrade, what are the impact and potentially maintenance task of any major release upgrade. This is the hardest part. Sometimes it might be best forgetting about using upstream container for some services and sticking to the version supported by your long term maintenance distro that does the job of backporting any security patch to have that peace of mind. You can still run it as a container, but using the distro packages. That is what I do for databases for example.