Visa. Can I leave the airport when in Shanghai to get a hotel for the night?

You can use 24h twov, but leaving the airport is no longer possible if your layover is less than 24 hours regardless of nationality. Some reported that bringing a hotel reservation will help. You can have a try.

Your itinerary doesn't qualify for 144 hours free transit. If you are staying more than 24 hours in China then you'll need a visa, and therefore you will have no problem leaving the airport at Shanghai.

You have to calculate whether the entire period you will spend in China is under 24 hours (from arrival in Shanghai to departure in Kunming). If it's under 24 hours you don't need a visa and immigration will have to let you leave the airport (given that there is a domestic flight involved). If not then you need a visa.