Having grown up in a similar conservative Anabaptist community and now living near a large Amish community, here is my $0.02.
Rental car--absolutely! As other answers point out, members of Amish communities own their homes/farms but not the roads. Of course, be aware of the alternative transportation modes you will see, and slow down for buggies, scooters, bicycles and pedestrians. Remember also that most horses do not appreciate cars coming too close to them--keep a nice distance away from them to avoid causing accidents.
Cameras--if you try to take photos without permission, you are likely to have the unsettling experience of having the Amish turn their back on you. This is not because they do not know what cameras are or because they believe photography is evil, but because they take literally the Biblical injunction not to create an 'image' of anything. If you choose to take photos anyway, it is respectful to do so discreetly and make sure there are no recognizable faces in your photos.
Finally, realize that these are people just like you, who have chosen to live a very different lifestyle. They are friendly but reserved, and most members of these communities will do their best to answer your questions provided you are polite and respectful.