You probably didn't tighten the crank nut to spec and it got loose, then as it rode around on the shaft it ate up the threads, which allowed the PTO gear to move and it just kept snow-balling. Did you install the compression lock-washer the correct direction? what did you use to tighten the PTO gear nut?
As for the sprocket with broken teeth, that's no indication of power, its indicitive of a sloppy chain or mis-aligned chain, or junk sprocket. Hell, I run the primary drive sprockets on my 10mil and don't have a single issue with broken teeth.