I have mine bored to 685cc (to fix the 2008 oil burning issue) no other engine mods, so I get a little less than I used to. Fully loaded (me bags/gear etc) ham fisting it, I go about 350km till I hit reserve and have about 50km after that before full empty.
Handling is fine, I found having an aluminum backed hand guards helped a bit with highway stability. Some people install a smaller fender for highway and high winds. I'm fine with it. Some also install a fork brace I haven't bothered.
If it is your first bike, try sitting on a bunch of different styles and see what fits you best.
It is by no means a sport bike, but still fun to ride. I like the height and upright riding position. Easy on knees.
One mod that MUST be done on KLR 650's the "doohicky" & it's spring must be replaced. THe factory part is wear. Very very very well documented. Use only Eagle Mike replacement parts for this.