1. I would suggest that you buy your JR voucher outside Japan, i.e. your home country before departing for Japan as it is 10% - 20% cheaper. 2. Once in Japan, you can exchange your JR voucher at any major JR train stations for your JR pass. 3. You can also make reservations for Yufuin no Mori at the same JR station counter and other reservations for your Shinkansen rides.

Latest schedule show a little faster, 3.5hr - 4hr via Kokura, effective from Mar 17 to May 7.

We went round trip because the train itself was an attraction for us -- the service is great, and the chance to view the scenery out of the front of the train was something really unusual. Very comfortable train. I'd recommend that you ask for a seat as close as possible to the very front of the front (leading) car. If there are seats available toward the very front (front row or second or third row) for one way, and not the other, then definitely at least get the seats on the trip with the seats close to the front. The Yufuin no Mori is not as fast as the Sonic service between Beppu/Oita and Kokura/Hakata -- it doesn't have the tilting technology, it's diesel and not electric, and it doesn't get the priority that the Sonic service does. So, if you want to get back faster, take the Sonic service one way and the Yufuin the other. Due to damage to the track on the train's traditional route, Yufuin no Mori is routed via Kokura at present.