Jiangsu Nanjing Airport Layover

Hello,
I have a 14 hour layover at this airport from 7PM-9AM later this month; is it safe for two women to travel outside of the airport in these hours? If so, where would you recommend locally to check out. Also, since, its a layover, do we need a visa - we are coming from the US? Finally, if we wanted to stay at a hotel nearby, are there any that you would recommend, and could we book the hotel when we get there, or should we do this in advance? Thank you so much for any information.