Checkin online for both flights. The agent in EDI will be able to give you paper boarding passes for EDI - LHR and LHR - JFK if you want.
The chances of a free upgrade are, in general, very low and it’s not worth getting your hopes up. You might be offered a cash upgrade online in Manage My Booking or when you checkin.
Cant comment on the ‘gourmet’ meals.
Enjoy NYC.