although an FAA PPL is automatically good for night the 'piggy-back' licence you'll have is only good for day VFR.
FAA Piggy-back now includes night - if your original licence does.
If you get an FBO to help, you're morally tied to him. You've got plenty of time to get it on your own - then you're free to look for the cheapest deal for your hours.
You'll be hiring a car, so getting to an FSDO should be no problem.