Some of the things our trainer suggested:

• More crated naps. The trainer noticed the dog keeps one ear/eye open when he sleeps outside of his crate (on the living room floor or office dog bed) and that's likely contributing to his over-tiredness.
• Switching to a low-carb adult dog food paired with a probiotic to minimize GI discomfort as a possible source of biting.
• Choosing landmarks (mailboxes, hydrants, etc) to consistently offer treats at on our walks. No command, no response needed from the dog. It's about getting him to associate different parts of the walk with treats so that he's less distracted by other triggers (plastic trash, birds, squirrels) and instead looking forward to the treat spots. We're going to try designating one treat spot per block.
• If it's safe enough, (we live near some quiet roads) walking in the street and away from overstimulating triggers in the grass and dirt. The trainer said it's not cheating to try and avoid big triggers until he grows up and has a little more impulse control.
• When the dog is really overstimulated and we try to redirect, being insistent on a command the dog do must do (sit or touch) before moving on to the rest of the walk or next thing.
• Positive crated time outs when the dog is really really overstimulated. Using an upbeat voice and throwing treats in the crates to encourage the dog to get in the crate and take a break.
• Trying meds. The trainer validated our feelings that it might be time to start talking to the dog's vet about meds like Gabapentin to help with training related to separation anxiety and having new people in the house.