Perhaps I can shed some light into your questions as I work on TBD since 3 years now.

In our case there are no Pr's, we push to master, the test suite is triggered, the dev environment receives the new code. It moves to other environments if the tests pass. We release to master using a canary instance that gets only a small share of the traffic, if our metrics for success fail then we rollback and start a hotfix. Yes you can have as many branches you want in your local but in the remote there is only one.