Consider hiring a car , you will need an International Drivers Permit .
Hiring is not overly complicated and Pick up at starting location and drop off at your destination is common-place.
I have used Times, Nissan and Toyota.
Its been a while and a lot of the sites now have an english presence , but TOCOO is a great place to start.
Note: Most highways/Express ways require a toll to be paid , an ECO card is required ( TOCOO can provide this) else have plenty of cash (a must) and you can pay with cash at the toll booth. ;
The speed limits on the expressways are generally between 80Kmph an 90 Kmph. The speeds on the local roads is generally between 40Kmph an 50 Kmph.
The expess will hugely shorten a trip , but will be expensive . As an example , Nagoya to Nagano is approx ¥12,000.
The best thing about expressway travel is the rest stops . There plenty of good food , showers , toilets and souveniers. Local produce and products are heavily promoted