https://github.com/frappe/frappe_docker/blob/develop/docs/multi-bench.md this setup is combination of multiple files and uses nginx to manage letsencrypt.
the ./docker-compose.yml and traefik is used in single bench setup, https://github.com/frappe/frappe_docker/blob/develop/docs/single-bench.md
In case of single docker-compose file, it includes traefik already, creating it again will cause error.
Use docker swarm setup if you plan to have multiple sites and multiple stacks.
Recently someone from community managed to build a custom stack out of official images. check this post Docker Installation - #5 by suodrazah you can check how that works if it helps.