Is it necessary to build upon the minimum in tasbih and to repeat any word or stutter that was incorrect after the prayer?

If you doubt the number of incantations, then build upon the lesser number as a precaution, because the default is the absence of increase. As for error or stuttering in theathan, you repeat it to obtain the reward, but it is not obligatory for you to do so, as these incantations are not originally obligatory.