If you just want to explore one country or region you could just buy a local bike, do your trip then sell it off before you go back to school. Fly in, fly out.
Next trip go someplace else. India, Chile, Thailand, Cambodia, Russia. You can buy a local bike in any of these countries, or rent one. That's what I did but I didn't have much time as I was working.
If you want to have your bike become your whole life and spend years on the road then perhaps a different approach is needed. Then you need to set the bike up for a lot of gear. I would go with a 250 four stroke of some kind.
The Yamaha's are good, but you also have the KLR250, XR250, DRZ250 and more.
Lois is in Africa now, on a new bike, an XT250. See her site for updates and buy her new book.
For more and better information on smaller bikes I suggest you surf over to
More Euro in focus and lots of folks using smaller bikes to do RTW rides.