Hi there and thanks for the post.
I am sorry to hear that you have lost your long time friend. Puppies can be a big handful but with patience and some training the usually do come around.
He may require a bit more strict training to help fix this problem. The positive method is great but some dogs just don't get the message. So you often have to encourage things along with a tap or flick on the nose.
Don't make it too hard but just enough so they notice and turn to you. At the same time continue the growling etc to make sure he gets the message. Water pistols serve as a great method to help as well.
Tke key is consistency......mixed messages just end up confusing and making things worse. So make sure everyone in the house and visitors as well know how to react when he starts nipping.
As for the lead issue it is about getting him used to the lead. The best way to do this is to try and create some positive experiences with it. Leave the lead around the house when you are home, play games around it (but not with it) and leave it around the food bowl.
This will help take the fear away from the lead.
Don't be rough with the lead at the start. It is a lot like getting a horse used to a saddle....it requires patience and a very slow progression to avoid problems
1. Do not punish your dog for reacting poorly to the leash.
2. Do not inadvertantly reward your dogs behavior either. Do not reassure your dog or give it treats, just behave normally and ignore your dog as if you do not notice its fearfulness.
3. Do not force the leash upon your dog.
If he is being aggressive on the lead then punish him for that....but if he is being fearful avoid punishing him as this will only make things worse.
I hope this helped please feel free to ask anymore questions as we are always here to help.
Todd