I have done this, but instead of PHP, I have used Server Includes, which is a performant and simple way to add repeating headers and footers etc without extra dependecies. Nginx, Apache and Caddy all supports Server Includes, but with different syntax. I have used Caddys templating language, which I am most comfortable with.
Proxmox does VMs and containers (LXC). You can run any docker / podman manager you want in a container.
Benefits of having Proxmox as the base is ZFS / snapshoting and easy setup of multiple boot drives, which is really nice when one drive inevitably fails 😏
There are still edge cases, but things have improved rapidly the last year or two, to the point that most docker-compose.yaml files can be run unmodified with podman-compose.
I have however moved away from compose in favor of running containers and pods as systemd services, which I really like. If you want to try it, make sure your distro has a reasonably new version of Podman, at least v4.4 ot newer. Debian stable has an older version, so I had to use the testing repos to get quadlets working.
Yes! Well, kinda. You can skip Docker and go straight to Podman, which is an open source and more integrated solution. I configure my containers as systemd services (as quadlets).
Symfonium looks cool, especially the support for DNLA, but it is not open source and not available on F-droid.
Castopod is great for hosting a podcast :)
I think this is where Anytype (https://anytype.io/) is headed!
In that case, I can recommend minicomputer’s like HP EliteDesk G2 800 Mini. You can get them with a variety of intel CPUs, they can take up to 32GB RAM, they have slot for M.2 disks and a regular 2.5" SSD – and they hardly use any power when idle, between 5 to 10 watts, depending on the CPU and CPU governor settings. They are sold used for ~€50 and if you buy newer generations you’ll get even more umpfh for a bit more cash.
In other words, very competetive with the Pi’s, only more available, cheaper and about the same power consumption!
It actually works great for slightly more complex stuff to, like converting markdown to HTML etc. Caddys documentation is made using Server Includes for example.