The best times to visit Tunisia are spring and fall. Our trip was in December, the rainiest season, especially in coastal areas. We had some wet afternoons and evenings, but never a steady downpour. Temperatures ranged from the mid-60's to the low 70's, dropping to the high 40's to low 50's at night. There are no nonstop flights between New York and Tunis, though Tunisair is supposed to begin this service before the end of the year.
Some travel companies based in the United States can arrange complete custom itineraries in Tunisia.
Hotel concierges may be able to arrange for English-speaking drivers or guides. Some of these agencies will also rent cars with drivers. It is a good idea to be sure that luggage will not be exposed. The roads are generally good, except in the desert, and well-marked with signposts in French and Arabic. It is best not to drive after dark.