You sound like a very loving owner! Your dog is very lucky
You do not need to worry about there brains growing to large and crushing the skull, that is a very big MYTH, as far as chemical imbalances of some kind?, that is very rare, and i doubt you would have to worry about that. He is at the age where his true temperament is showing(mature) so if he is friendly and loving to all people, he won't change, or "turn on you"
And yes, many dogs hate getting their nails done!!