Just sand enough to smooth the glass. Don't sand down into the fiber. The longitudal cracks are just stress cracks, they don't hurt anything. But, you might not be able to cover them up. Don't try to sand them out, though.
That number is the serial number. The model will be written on the limb; Kodiak, Kodiak Special, Grizzley. If it is osage he should really think hard before you gring the handle. If it is an osage,"Grumly", he will be crieing when he finds out how much it "used" to be worth before the Floppy rest and modifications. If you can send me some pictures or post them I'd be glad to help Identify it.