This is a recent addition to support having dedicated status for multiple agents. Please consider this as an implementation detail.The correct way is to retrieve the replication status via the Replication API, see an example in https://experienceleague.adobe.com/docs/experience-manager-cloud-service...
Just re-reading this: That path belongs to classic UI, and there you have to set the ACL into /libs, and there's no other way. With TouchUI you can work with renderconditions to conditionally display elements of the UI.
you need to setup your dispatcher configuration in a way, that only "official" hostnames are allowed; anything else should be redirected to your "main" domain name.
This is only relevant if you plan to use the Language Copy functionality, check [1] for it. [1] https://experienceleague.adobe.com/docs/experience-manager-cloud-service/content/sites/administering/reusing-content/translation/wizard.html?lang=en
If it works locally we can most likely rule out major coding issues.The easiest way to deploy a custom agent to publishs is probably to include it a deployment package. The next best is to create it on author and then replicate it (can be done via CRXDE).