To check the ECU's codes go here:
http://www.nicoclub.com/articles.php?id=60332
I would see what pops up
Then I would think you have to do the under plenum hoses because I take it its cold over there by now or when ever its cold you smell gas right?
I would also get the service history from one of the nearby Infiniti dealers and see whats been don on the car.
But it might be a leaky O ring on one of the injectors, Hope its an easy one. Or it could be the under plenum hoses.
Either way good luck and Welcome to NICO.