Yes. 127.0.0.0 is the localhost. This is the IP the container is listening on. Even if there was no firewall it wouldn't allow any connection except from the host. If it's set to 0.0.0.0 it means it'll allow connections from any IP (which might not be an issue depending on your setup).
The reverse proxy runs on localhost anyway, so any other IPs have no reason to ever have access.
Yes. 127.0.0.0 is the localhost. This is the IP the container is listening on. Even if there was no firewall it wouldn’t allow any connection except from the host. If it’s set to 0.0.0.0 it means it’ll allow connections from any IP (which might not be an issue depending on your setup).
I assume #2 is just to keep containers/stacks able to talk to each other without piercing the firewall for ports that aren't to be exposed to the outside? It wouldn't prevent anything if one of the containers on that host were compromised, afaik.
I was getting more at stacks on a host talking, ie: you have a postgres stack with PG and Pgadmin, but want to use it with other stacks or k8s swarm, without exposing the pg port outside the machine. You are controlling other containers from interacting except on the allowed ports, and keeping those port from being available off the host.