1) It's a. Generally speaking, the みたい that means "seems" inflects as a 形容動詞 (and I suppose should be referred to as みたいだ), although some people, because of the い, will inflect it as a 形容詞. However, it will follow a verb's 連体形 (or 辞書形), not a connective form. That's the dead giveaway that it's the "try to..." auxiliary.
2) I assume so. But it's hard to know for sure without context.
3) Japanese people in general.
4) It's その人に、「日本人は違うな」と思ったかどうか・・・
5) It is the former, and you are correct.