Could Bismark in a united Germany become a new Napoleon?
No. Bismarck and Napoleon were two completely different people in two completely different situations.
Napoleon: Military genius, glory hound, extremely ambitious, wanted to take the greatest power in Europe and make it even greater, didn't know when to quit, pissed off every other power in Europe, rose to power in a time of stability, overturned the status quo and made a new one
Bismarck: Diplomatic/political genius, definitely a part of the status quo in Prussia (the Junkers), Prussian nationalist, knew when to quit, more concerned with Prussia's prosperity and strength than establishing some vast empire
Most importantly, Prussia/Germany already had a King/Emperor. Bismarck wasn't in the position to become Emperor, even if he wanted to be.