"Considerably" is an adverb.
Yes it can
Yes, adverbs do modify other adverbs, for example 'He slowly, carefully fit the intricate pieces.'
Yes. It can modify another adverb.Thanks for asking your question.Bye Bye now.
The very new video game has sold out. the verb is - has sold out (present perfect, main verb sold out) adverb #1 is - new modifying video adverb #2 is - very modifying new