Mostly for formal sentences; however, it is good to learn as our accents make it less obvious when forming questions without this bit of clarity.
Because you included the question mark your version is also correct. Without the question mark your version would be a statement; whereas their version would still be a question (lacking the appropriate punctuation). You should still report it.
As long as they're referring to different persons, it's okay. For example, if "saya" (first person formal) is used, continue using it for the rest of the sentence. If "kamu" (second person informal) is used, continue using it for the rest of the sentence.
In this sentence, "kamu" and "saya" is used in the same sentence because they're referring to different persons (second and first person respectively).