I've had a Tengai for a few years and use it for travelling;
- Centrestand - there was no official Kawasaki one that I know of, but any of the aftermarket ones (Dual Star, Happy trails etc) designed for pre-2007 KLR's will fit as the main frame on the Tengai is the same as all the A or C variant. I can't give an opinion on them though as I have never bothered with one.
- Luggage - there are lots of pannier racks (for both hard and soft luggage) around for the standard KLR model A but here you have to be careful. If you study the pictures of them you'll see they normally mount at the lower end to the rear foot peg carriers and these are quite different on the A, where they are part of the sub frame, to the Tengai, where they bolt to the main frame. Bottom line is most will not be suitable without some sort of adaption.
Hope this helps.
Despite being old Tengais make great travel bikes - enjoy yours.