Microservice SDK (java) best way to call unsupperted but available REST endpoints

Can only comment on your first question…

Where is the best way to get the different parts of the url?

The platform URL should be available as environment variable C8Y_BASEURL.

See here: “[…]The Cumulocity IoT exposes the REST endpoint /user/currentUser. The microservice retrieves the Cumulocity IoT address from the C8Y_BASEURL operating system environment variable.”