Yes, portainer will see every container you make, regardless of how it was created.

No, creating a docker container doesn’t make a compose file. It’s like cooking a meal doesn’t output a recipe.

You can save the compose file(s) wherever you want, you just need to run “docker compose up” from that directory. If you make the container within portainer, I believe it stores the compose files in its own volume. Not sure about that, I keep my compose file separate from docker for most services.