I also see small amounts of different colored particles, like dull red, yellow, even some green ! You must have gotten the Honda, Suzuki and Kawasaki flake oil additive. The steel is probably the crank big end rod bearing. I just bought a used WR bottom end and the only bad bearing was that one. The sand might have come in from the breather tube. I don't know about the rest of the garbage. Maybe the clutch as mentioned before or timing chain guides. Are there any funny noises? If not, put a magnetic oil plug in it. Ride it and see if it breaks or take it apart now.