well remember that $leaves is an array. So you need to give it an element in the array to constrain to. I'm surprised that using $leaves as you are even works

so you need to do something like

pointConstraint -offset 0 0 0 -weight 1 $leaves[5] $new;


or you could build up a string like what you have done for the $new variable where you add a suffix and stem to a randomly selected array index. does that make sense?

And as for resources I never bought a book or anything like that. Giving yourself projects like this and using the mel script resources are the best ways of learning IMHO

Alan