1. In my opinion 2.5 to 3 hours between the flights.
2. Use the air trains located at every terminal it is fast free and easy.
3. Terminal 4 is open 24/7 for you to stay and that is the terminal which you will arrive upon at JFK airport.
4. There are some smoking huts outside every terminal.
JFK Airport Guide
1. In my opinion 2.5 to 3