Sweaters and Suits/Blazers

Question.

I was wondering what the rules are for wearing a sweater with a suit or blazer.

1. Can you wear a sweater under a suit? I'm inclined to say no, but I wanted to check.

2. I'm guessing its okay to wear a sweater under a blazer or sport coat, but I wanted to check. Also, is it okay if the sweater has a collar.

As an example, here is a sweater I have.
https://www.brooksbrothers.com/IWCa...7477&Parent_Id=305&default_color=Blue-heather

Thanks for the help.