American Kennel Club Anti Anxiety and Stress Relief Calming Coat for Dogs, Small, Blue

What size dog does a size medium fit - I don't see any specifications (weight of dog) to help me determine which size I need.

my German Wire Hair is afraid of people in general - going for a walk, people coming into the house, he wants to run . Will this calming coat help?

Can a male dog pee in this? I'd love to get one for my Derby but he'd have to be in it all day when I'm at work. Thanks.

Will this help with my mini aussie that gets over excited when people come to visit?