너무 is to a great extent, and fits the "too much" role of adverb. 많이 usually refers to something you can count, usually meaning many or "a lot of" in the role of adjective.

"너무 많이" in place of "너무" is now accepted. However, it is redundant so I would not say it's a good translation.

많이 is an adjective for" a lot/many" while 너우 is an adverb that means "to a great extent" fitting the role of "too much" in this context.

많이 means "a lot" but does not have the same meaning as 너무 which is "too much" or "excessive". So yes you could, if that is what you are saying. But in the case of ,"too much" 너무 is used

No, the negative is "~지 마" plus whatever formal conjugation

because that'd be informal. and the skill is about formal conjugations. but that is correct as well!