OP: ........I would add to this :.......AND knew what I was getting myself into ..... ( do you?) .......

then I would say fly to CTS, WKJ, AKJ or somewhere similar and point the car away from the city and go. You said you want a long drive -- you can drive a long way in Hokkaido and it is absolutely wonderful. If urban regions are your idea of scenery, don't bother driving

As mentioned earlier, try to get an English GPS (unless you are fluent in Japanese) as it will help a lot (I don't know if an English version is even available) ..... and / or some really good bilingual maps. In rural Hokkaido, that would do for the most part. Finally, if you are going really far afield, you might want to rent a cell phone (though who knows if you will be able to understand the person at the other end).

International Driver's license is not optional.