There is a large/big number of students.

1. There are a large number of students.
2. There are a big number of students.
3 There is a large amount of water.
4. There is a big amount of water.
5. There is large amounts of water.
6. There is big amounts of water.
7. There is an amount of water.
8. There is amounts of water.

I have several questions regarding the determiner 'a number of' and 'an amount of'
1. Is it correct to say 'a big number of something' like sentence 2, 4, 6 instead of 'a large number of'?
2. Is it correct to say 'large amounts of' instead of 'a large amount of' like in sentence 5. - If it is are they the same in meaning?
3. Is it correct to say 'an amount of' instend of 'a large amount of' like in sentence 7? - It it is, how about sentence 8?
Thank you very much teachers.
P.S. The reason of my 3rd question is that we usually say 'a mumber of' wthout 'large' to mean a great quantity of objects.