A sighted person can visually inspect themselves in a mirror to compare their real physical appearance to their idea of what they look like. They have a reference point to ground their perception of their appearance to reality - granted they have limited use for this reference point because they have trouble judging what they see in the mirror objectively, but it's still there.

A person who can't physically see the reflection of their face in the mirror has no objective reference point - they have to trust other people's perceptions of what they look like. People all have different types of looks they find attractive - so you would would not get consistent feedback from others on your physical appearance, and you would have no way of comparing what they see to how you see yourself in the mirror. I can see how being blind might exacerbate body dysmorphic disorder - interesting question, OP.

Yes same as those born blind can be trans, we can have the same issues as the sighted.

Yes, they can be. I've worked with a few clients who have had them before.

Keep in mind that body dysmorphia is about perception of your body, not reality. Now imagine their classmates make fun of their large nose (or whatever, it doesn't actually matter). They often can't really compare it to others, so they may assume what everyone is saying is true and internalize it.

Uh...good question! I knew a girl who was born blind who struggled with anorexia for many years. But Wikipedia tells me that's different, and then doesn't really explain why. Still, I'd think the answer is "yes". I don't really know what I'm talking about though, so take that for what it's worth.