Assuming for a moment that you do not have luggage check…
(With luggage – with delivery times up to one hour at BCN at times – this is near impossible; but even without checked luggage the correct answer is of course: “fly to BCN the day before”, unless you are on a flexible ticket to JFK.)
Over here, it is Vueling that has the bad reputation when it comes to delays, but the morning flights are indeed generally OK. (Have you checked the on-time performance for these on Flightstats?) And since Norwegian also has the earliest flight, it seems logical to choose them. But…
Norwegian uses terminal 2 at BCN. I am guessing that you are flying from T1 (since I don’t know of any JFK flights from T2), so using Vueling would put you at the right terminal on arrival. (There are no airside inter-terminal transfers at BCN.)
The transfer itself is easy walk from the gate to the central area of the shopping mall (sorry, terminal), up the escalators, passport control (which can take a bit longer than usual since April), go to gate. (Some US flights leave from a separate area at the end of the B gates, so no need to walk to the central area, but the process is the same of course).
And if you really want to choose the airline with the best on-time performance… ;-) Ryanair also has a 6:30am flight from PMI to BCN, but they use terminal 2 as well.