Hey Chris,
Welcome to the site.
There is enough info on the 5oo here a guy with some gumption could write a book!
The bike in stock form has plenty of power to move around a guy your size alright.
The problem usually is setting up the bike to fit Xtra large riders.
Larger higher bar bends,bar risers and offsets, longer clutch cable and brake line. Larger footpegs with offset and I imagine a longer shifter would be a plus.
Re springing the bike for your weight and riding style will help.
Last but not least is what you will need for Horse Power. Just like any other bike, the hotter you build it, the narrower the powerband tends to be and the reliability factor starts to dwindle.
With around 60 pony's on a fresh engine, there is enough power even for a guy your size to have fun.
If you use good parts, and quality workmanship the engine will give you years of service.
Maintenance is key to good service life, just like most anything I suppose.
Get your self a Clymer or Kawasaki service manual so you can see what all is going on with the bike.
Here are a few examples of both:
http://s69.photobucket.com/albums/i75/Friar-Tuck/KX%20500/http://www.kxriders.com/coppermine/thumbnails.php?album=lastup&cat=1&page=3Tuck\o/