You have a number of items, so definitely use "are". For "there is music, art and English class in my school", this sounds shoddy. Did you read this somewhere? I'd rewrite it using "are" and "classes", unless I actually meant that there is a single class of music+art+English in one... which may be unlikely.

I agree with the above answer. for your second question:There is music, art and English class in my school....My favorite subjects are music, art and English." Why use "There is..." not "There are music ,art and English". There are 3 kindda classes. singular subject uses a singular verb = HE IS smart plural subjects uses plural verb. = but THEY ARE smarter. In the case of "There is music, art and English class in my school.." you use IS because you are presenting each subject as its own individual form. Sometimes it's all about how you see the subject: Significant exploration and development is underway to exploit Australia's substantial gas resources. Here, exploration and development are treated as a unit taking the singular form of the verb is. More examples: There are lot of things to eat here. There is Chinese, Italian, Korean... These are my friends from New York. This is John, Kate, Josh...

May favorite subjects are A, B and C.

Everyone gave a brilliant answer above!

Don't forget the comma before the "and" "My favorite subjects are music, art, and English."