You could create a fresh container, install docker, and create a new template image from it. This way the overhead of installing disapears. The overhead in resource usage for each docker installation would remain the same as before.

As mentioned in another reply, you could run several container in one lxc. For example with docker compose or podman. Since I have no experience with podman but with docker compose, docker compose is pretty simple.

But all in all, I prefer to install everything “bare metal” in lxc containers. The main reason is, I don’t want to mess around with the extra layer of configurating ports etc.