I've tried an POM run as Hamburg. It was quite fun at first. Doing constant Humiliation CB war to gain all the MP for developing, having Ditmarschen as March, and claimed my way to Danzig with the Age ability and sniped them when the TO got attacked by Poland and released them to a Baltic trade port. It's somehow strangely satisfying to be considered a rival by a fully grown Poland Lithuania who actually expanded a bit into Russia, a Denmark with it's Unions still intact and an Austria that got the Burgundian inheritance and Great Britain while your still an OPM.
At some point my dear ally the free city of Bremen couldn't stand my dabbling around as an OPM anymore though, they conquered all of northwestern Germany, became a monarchy and got them self elected as HRE after the league wars. They actually showed a remarkable skill in AE management while expanding in the HRE, every time I checked whether I should ditch them yet to prevent a coalition war, they had like 48 AE with everyone.
At some point my dear ally the free city of Bremen couldn't stand my dabbling around as an OPM anymore though, they conquered all of northwestern Germany, became a monarchy and got them self elected as HRE after the league wars. They actually showed a remarkable skill in AE management while expanding in the HRE, every time I checked whether I should ditch them yet to prevent a coalition war, they had like 48 AE with everyone.