Most authors don't give out their personal email addresses to the public, for the same reason they don't give out their personal phone numbers. If they answered every email from fans, they'd have no time to write their next book.
If you find an email address on an author's website, don't expect a prompt reply, or any reply at all. The address will probably go to the author's publisher or agent, rather than direct to the author.
You stand a better chance of getting a useful response if you ask specific, focused questions that are not answered in the FAQ section or by two minutes with Google. That minimises the amount of time they have to spend helping you. Don't ask vague questions or request an open-ended commitment to help. Pick several authors to ask, because most of them aren't going to want to help you with your homework anyway.