Our coton is a brat

Our 16 month old coton is well, what shall we say...a rather high maintenance brat. He runs from us every time we go to put on his harness for walks unless we give him a treat each time. If we are not fast, he will take the treat and then run also (a thief). He constantly picks up sticks and other things that he should not have and eats them. I try to get him to release them but he won't. I do have some bitter apple spray in a bottle and he knows if I get that spray out, he usually spits out whatever he has in his mouth (I am afraid he will get an intestinal blockage otherwise). But it does not keep him from picking up another stick 2 seconds later and we repeat the same thing all day every day.

He is the most friendly dog I have ever met; he loves to see all people and he loves other dogs. But he is an immature brat most of the time. On top of this, he is the energizer bunny, never really takes naps now nor in puppyhood (even though the literature says puppies sleep like 16 hours a day - NOT! Not this puppy, neither then nor now). Even though he is a very happy dog, he also is a nervous dog - whenever he gets anxious for any reason, his first reaction is to mouth or bite us. He is also compulsive - will dig frantically at bed sheets or blankets or the carpet. I think this stems from his nervous nature but that seems to be in his DNA. It's just who he is unfortunately.

We took him to dog training as a puppy for 4 months and I prayed for the little fellow. Finally at 6 months he was neutered (can you believe it, about a week before he got neutered, he started urine marking in our house! I was beside myself, never had a dog that we owned do that before.) It all helped, he is better now than when he was a puppy but he is still a little brat.

Our other dog was such a sweet mellow gem but he died. This is the new guy. We give him the very best in life, great food (I mean REALLY great food - all homemade, gluten free and I also bake him homemade dog biscuits), lots of walks and he is home with us almost all the time since we work from home. When we do leave him alone, he barks and barks and barks (separation anxiety) and just all around has a fit because he is mad/anxious that we are leaving for any length of time at all. I take him for walk before we leave, still no matter, he has a fit that we are leaving. Any suggestions? We train him but the problem is not that he does not know the right thing to do, it's that he ENJOYS being a rebel. Sometimes we laugh and just shake our head, but other times when we are tired of all of his shenanigans, we just wish he would grow up and wonder if this is how it is going to be for the next possibly 14 years with this guy. I wish he were a mature mellow dude. He is the complete opposite of our last dog.

Are most cotons like he? I thought they were all mellow like our last coton who was such a gem.