If your using postmount brakes, you can use alu. bolts to hold the caliper to the frame/fork. You can also use 3ti/3alu. rotor bolts. Swap any other bolts to Ti. You could also use alloy backed pads, but those are usually organic, which won't last long in mud.
If you have quite a bit of patience, you could sand the calipers down, like this guy:http://forums.mtbr.com/weight-weenies/t ... 52294.html
Ashima rotors should work fine. If you want the absolute lightest, have a look at Scrub components.
If you wanted superlight, you could go with Extralite hubs to save even more weight over the Prince/Princess, but I don't really know how durable they are. You also don't need thicker spokes. I know plenty of people who use DT Revo's/Sapim Laser on their MTB's, all of them are 170lbs+. I've even heard of downhill racers using light weight spokes (CX-Ray's, Revo's, Lasers, etc.) They may need to be longer, depending on how you had your previous wheels laced, but that will add very minimal weight. IME 2x non-drive side front, radial driveside front, and 2x all the way on the rear will be fine.