-) search the WWW for B369, which at one time could get you to UHMD Providenyia at least, in a more or less organised manner.
-) will work better if you spell Magadan correctly - but without consulting a map, I think you don't need to pass there. Anadyr would be on your route, and from there I should think you could get to Petropavlovsk directly?
-) when planning, do not forget you will be crossing the date-line