I wana know how long do I need to reach Changsha from Singapore

It takes no more than 5h on a direct flight. As I check, flight is available in the early morning or late night, only one per day. So you can arrange according to your demand.

It is hard to know the number of villages in the city, but the nearby Tongguan Ancient Town and Jinggang Ancient Town are recommended, both of which are around 19mi (30km) away.