Assuming that you are the one wearing the blazer, you would ask, "How do I look in this blazer?"
If the blazer was next to you (on the table, for instance), then your question would be, "How do I look with the blazer next to me?"
"I am home" is correct. "I am in home" is grammatically incorrect. For the sake of comparison, your second sentence would be, "I am at home."