CAN is a pretty new nice airport. Domestic and International are in different areas in the same airport building. It is a short walk from international arrivals to domestic departures. 3 hours should be plenty.

Never tried it in CAN, but usually you cannot check luggage thru to domestic flights in China. At least i never was successful. You need to clear customs at CAN. Not like in Europe where usually you clear customs at the final destination.

Lounges typical don't have much food, the eating places inside are typically dramatically overpriced. If you want something to eat look for some place outside security.