+1 on the mx51's they are ****** sweet! they replace the 765s. the mx51s are great on any terrain, i ride a real hard packed track and they rip, and then when it rains and is a muddy mess they are still decent. i cant reccomend a better all around tire.
i ride a worked yz125 and love it, get used to throwing it around and have a blast with it. nothing is more fun that mx when it finally clicks. its the one motorsport that i found is constatntly challenging me, there is always a way to go faster and ride better. good luck!