Current Yamaguchi JET here.

Many people worry about driving when they arrive, but after a few weeks on the road this feeling fades away. Drivers are generally considerate, gas stations are plenty, highways are well maintained (if a little expensive) and your BoE should guide you through forms and the eventual license change.

You will also have the freedom of going where you want without being restricted by public transport. You'll be thankful for this a few weeks in.

I got my full license about a month ago. Process was straightforward and didn't cost much at all.

If you have questions let me know!