wtf ?!?! where do I get a pet dog ?

all the way to 81

50 is the "easy" level cap, after that supposedly leveling takes longer (more skill points before you get the level up)
but yes, 81 is the cap, but even with that you can't max out all the trees, but it is nice if you messed up somewhere or wasted a point here and there

I used to max out allteration. Then I took an arrow to the knee.

Is there a skill tree more worthless than illusion ?

illusion has invisibility.
i find lock picking slightly useless, considering you can crack any lock fairly easily.