What are the implications of subscribing to the same channel as the one I'm publishing messages to?

Everyone connected to a channel will always receive all published messages regardless of who published them. Often, building an app with a single channel per room of users is the best way. To decipher the message publisher, you can include a sender_id key/value with each message.

When a message is received the value of sender_id key can be inspected to see if the message came from the subscriber - if so, then the message can be ignored by that subscriber (the publisher of the message).

Note: there is no requirement for a client to subscribe to a channel in order to publish on that channel.