I don't know what country you're going to visit and what not, but I've lived with host families, so I'd suggest something along these lines (if you speak or can write in their language, that's probably a plus):
Hi my name is so and so, I want to first thank you for inviting me into your home! I'm very excited to come and stay with you and learn more about your country and your culture. I have a few questions for you if that's okay. Do you have any children? What is your neighborhood like? How do you spend your free time?
I know it sounds corny, but its just to see how they respond, and gauge what they're like. After you hear back from them you can ask them more questions. Good luck!