Do you have a backyard? Introduce them outside of the house initially if possible. Show more attention to Derby than puppy. Yes, puppy should have his own crate. Derby's is Derby's domain...
With an 8 month old...I really don't think you'll have much of an adjustment between the two. Derby is gonna love having a playmate. Just be sure for a little while to give Derby lots of attention.
Ramsey was "first"...she got the first treat, she was let out...first. Now it doesn't matter who is first...
At my house...Ramsey and Reese slept in our bed....Reggie was confined to an x pen. Reggie cried...Ramsey and Reese paid him no attention.
I did...ME. Before a week was out...Reggie was in the bed too.