Is the emission of pre-seminal fluid (madhy) after a wet dream considered a sign of puberty and accountability? And is performing an ablution (ghusl) that suffices for wudu valid in this case?

The emission of fluid from you, whether it be seminal fluid (maniy) or prostatic fluid (madhy), is considered a sign of puberty. If you are unsure about the type of fluid, you may consider it madhy. In this case, performing ablution (wudu) is sufficient for your prayer to be valid, provided your wudu was performed correctly and has not been invalidated. Washing the hair of the head instead of wiping it during ablution is disliked (makruh) but does not invalidate the ablution.