hi,polina, They all are correct. In theory recently, "a geat deal of " is similar to "much", be used with uncountable noun,for example, ～people,～money, ～confidence... but,in the past,"a geat deal of "can be used with both of uncountable noun and countable noun,therefore, "i have a geat deal of friends" is correct. By the way, "a geat deal" can be used as adverb, for example,He smoke a geat deal . I'v learnt a geat deal from you....

They're all correct. a great deal of = (more than) a lot of and the grammar for both is the same.

The rule is the following": "A good deal" and "a great deal" are used only with uncountable nouns: I have a great deal to do. Russia exports a great deal of timber. He spends a great deal of money on his car. "A great many" and "a good many" are used with countable nouns. He has won a great many races.

is correct and that's when live

Use 'a lot' instead :p