1) okay. (Or you could omit "if I'm" both times.)
2) I wish there were a device you could point at people and you'd know their nationality/know where they were from. ("Was" is also quite common, though not really correct after "I wish.")
3) What's your shoe size? or -- What size shoe do you wear?
4)"Her house is closer to mine than yours" is ambiguous. Choose either "Her house is closer to mine than to yours" or "Her house is closer to mine than yours is."
5) Okay (although I don't really understand why these two things are mentioned together.)
6) "He trusts me more than you" is ambiguous. Choose either "He trusts me more than he trusts you" or "He trusts me more than you do."
I'm just curious -- may I ask where you get all these sets of sentences you ask about? Are they from your own writings or conversations, or from things you've read, or from some sort of grammar exercises?
Is (1) about Tourette's?