If you a checking your baggage through, you should check with AA and see what the Minimum Connecting Time is as it is their responsibility to deliver the baggage to BA.

The minimum check-in time at JFK for Y is 2 hours and F/C one hour although if you are in F, C or have status on OW you will find a separate security area at the rear of the premium check-in that usually only has a couple people in line at the most.

I dont think you can walk, but the train goes between terminals and the terminals are next to each other just separated by major roadways.

Your proposed times however leave no extra time in case of delay on your inbound flight.