No, "Hi" mean "Hai". They are a seperated word, but if you're using it to greet someone, then it can be the same.
"anda" is formal and "kamu" is informal and it seems that duolingo is teaching the informal bahasa indonesian.
I agree! Why not? That is the literal translation and it is something that works in English too. Not the most common way to say that but it is accepted.
"Hello, where art thou from?" When learning languages with a distinction between you (sg.) and you (pl.), I like to use the 2nd person singular thou.