Update: Lucas is doing much better. His inclination is to be naughty but he's holding back really well. He's learning the right way to play with others (and that if he plays the wrong way then he doesn't get to play). He's been facing his fears, learning to target things that make him nervous (like balloons in the wind), and generally getting over things and people that used to make him bark. With puppies every day is a new story, but if every day was like yesterday then I'd say he actually has it in him to be a good dog
Oh, and he also got neutered.
Here's a pic from yesterday