607 cutting it close, possible, though I wouldn't do it unless there were no other choices.

The earlier flight should be fine.

Tolls depend on which route they take, remember the lower Manhattan crossings are no longer HOV only anymore, so the driver may take an alternative route to get around some traffic and that may require the $ for a toll.

There are sometimes very long taxi lines or sometimes no taxi's at Kennedy, I'd shoot for the car service to be safe, and if they aren't there grab a cab.