Dont know how many peole have said the same thing I am about to say, but here goes nothing.
#1--Yes, over practise can harm your hand, same thing happend to me when I first got mine. I was so eager to learn that I couldnt put the thing down. As a result, my hand and wrist started hurting and the tips of my fingers were getting numb from trying to play faster.
#2--To use the 6, 7 and dotted 1 notes, press your hands lightly against the sides of the ocarina and curl the tps of your fingers back to lay them off the holes. This helps improve speed in your fingers as well. If you would like a few videos on how to better your holding, trying going to
STLOcarina.com
They have a lot of vids that help with breathing, holding and many other asspects f playing and mastering the instrament.
Hope it help ^^ Just aske me anytime ifyou need anything else