"I sleep a lot."
Translation:Mi multe dormas.
I realize this may be an old thread but your explanation might be confusing for new learners:
First, there's neither a noun nor an adjective in the given sentence, just a verb (sleep / dormas) and an adverb (a lot / multe).
Second, saying it does not make a difference in Esperanto whether to put the adjective before or behind the noun is just not correct. The normal position is before the noun. Onl put it behind the noun when you have a special reason, such as emphasis.