Getting a second havi! Need tips.

My havi (Quincy) is going to be 4 at the end of this month and I’ve been waffling on getting him a little buddy! I have an opportunity to do that in the coming weeks, but I’m having some anxiety around it because I’ve never introduced a puppy to an adult dog on my own.

Quincy is fine while I’m away at work. I do have a standard 9 to 5 and the office is a 7 minute walk away, but I can’t get out much. He is gated in the living room and kitchen all day and allowed to run wild when I return home (the crate training did not work because he was screaming at night like he was being slaughtered and I have neighbors and thin walls). With a puppy introduced, should I keep him in a pen elsewhere in the apartment while I’m gone? I’ve read a lot that they could comfort each other and play while I’m gone, which would alleviate separation anxiety, but should I be leaving the new puppy alone with the adult unsupervised? When would leaving them alone together be possible?

I’m happy with adjusting my routine and I’m prepared for some changes! I really need some tips because I’m nervy about not having any experience. I’ve had adult dogs together in the past, but never a puppy and an adult. What can I expect? How should I prepare? Any advice is appreciated! I’m probably overthinking this.