ZEROYAAMen's Long Sleeve Dress Shirt Solid Slim Fit Casual Business Formal Button Up Shirts with Pocket

My son is tall and skinny he is medium when it comes to shirts but I don’t want his shirt to be to big I want it just right on him he is 15yrs old

If My sons a Men’s size medium, should I get a size up?

Is the white shirt solid or cheap somewhat see through material? (Can you wear it without a t shirt)

I tend to get overheated. Is this shirt made from material that allows the torso to remain cool?