If your piston to cylinder clearances and ring gaps are within tolerance I would reuse the piston IIWM, especially if you're just trail riding. As kdxazz said, the cast unit will last a while under moderate usage as long as you do your regular maintenance, although I don't know where he gets 1000 hours since Pro-X recommends 12 hours, but certainly you could get 100-200 hours out of it as long as the rings last. They also don't recommend running their cast pistons in a chrome plated cylinder, so hopefully your sleeve is not. If you were to replate your other cylinder you're still looking at a new pitson/rings...unfortunately our hobby is not a cheap one anymore
Also as SS109 pointed out, you could stand to run through the jetting process once it's all back together. As for your crank...ouch. You could probably get it to a competent machinist and have the missing piece welded on and then turned down and threaded. They would also need to notch it for the Woodruff key. Not surprised it is still on the broken shaft as it is a tapered interference fit, but am surprised you haven't spun the flywheel as the keyway appears to have departed with the missing part of the crank. No way you put it back together and ride it that way safely as there is no way to torque it down. Best bet is to find a crank either on Ebay or elsewhere, cheaper than buying an OEM one (though you can still get crankcase halves and have a competent crank reman build it back up).
Finally, the whole "I know [insert race/country/sex]..." generalization has no place on this or any other enthusiast forum and does nothing to further all of our members enjoyment of our collective passion.
