The difference is a bit subtle. A statue is a representation of a person or an animal but a sculpture is probably most associated as being a piece of art and may or may not be a person or animal.

No, it is not correct but maybe you mean:- Rosa knew Peter before she meet John. or maybe Rosa knew Peter before John introduced them.

major

I understand your sentence but it is not correct. Some examples: My exam result was less than I thought I should get. My sister has less money than me. We had $40 less than the bill.

A brook is generally a very small flow or river so I think that the use of brook and mountain are too different in size. Also serpentine would not be used but snake would be quite common. Maybe "The river snaked through the mountain"

I regret going to the party because it was so boring (or dull) There may be some countries that flat would work but I have never heard it used like this.

http://theoatmeal.com/comics/apostrophe

I wouldn't have done something like this before.