1. They don't use sleeves. They can BE sleeved, but they don't 'come' that way. Just because the piston is replaced doesn't mean there needs to be any replating, unless the plating is damaged or the bore is damaged. More often than not the piston will wear beyond spec before the cylinder is damaged. Of course, unless things are let go TOO far. It's not chrome, but a hi-nickle plate, hence the name nikasil. Also referred to as nicosel, nicosil and such. The first is the trademarked name.
2. Kawi recommends 32:1 fuel/oil. That, like the oem jetting, is on the safe side. More commonly, 40:1 is used. Oil mfgs like maxima recommend 40:1. That's not based on it being a kdx, but size of the engine. You can find that @:
http://www.maximausa.com/
You can get a manual from any kawi dealer.
Do bookmark (and check out) CDave's site:
http://justkdx.dirtrider.net
A lot of info on basic mods, carb theory, links to good spots etc.
You might ask if a wiseco piston was used. If you've been looking around this site much of late, you've read about the 220 oem piston. It's got problems, and should be replaced certainly during anything called a 'topend' job.
If you have some other questions, please do ask. Better to start another thread, though. Something that will contain responses pertinent to your particular question.
Have fun!!