I believe Princep (actually Princeps Senatus) was not an office but rather a title. It was of ancient republican heritage and was often given to the leading senator. It meant “first among the Senate” and carried no additional powers or authority beyond other offices the Princeps might hold. It was not dissimilar to our own President pro tem of the Senate, which is also largely honorific.
In the later imperial times it became one of the emperor’s titles (like emperor/imperator for that matter) despite its republican heritage. As such it eventually turned into the title Prince or its equivalent in all other European languages.
Augustus was also a title or honor, not an office.
For most of the time he was emperor Augustus held no particular office in the rather rickety Roman system of government. Rather he held a number of powers delegated to him by the Senate, as had previously been often done for other senators.
The sum total of these powers, in particular his absolute control of the army, gave him autocratic authority but this was concealed by their diffuse nature, so that during the first century or so of the Empire (called by historians the Principate) it was still in theory a Republic, not an Empire.
good points — I think the disguise of the Principate continued until 3rd century when an Emperor divided the Empire 4 ways (what was his name, starting with D)