It is GRAMMATICALLY correct; nevertheless, it does not sounds natural, to be honest. I would say "各种文化之间的差别很大。"

对的 :)

You should add an adjective"不同的(different)" and a verb "有(have)". "不同的文化之间有很大差别“ sounds native. We often use adjectives to make it clear and keep it balanced. Here's a rule: Put the key word at the end of a sentence. Generally speaking, the key word is often a noun.

sounds strange

'Very' is cheap. You can say either it is 'very' cheap or simply cheap without 'very'. 但是说中文的时候，“很”时必须的，没有“很”听上去很不自然。