with regards to hierarchy comments
But I would also say that it's not your place to establish a pack hierarchy between your dogs. Dogs will generally work it out on their own - some groups of dogs will have a clear leader, for others the leader varies depending on the situation... you working to maintain an arrangement that may change at some point could create more stress.
I think that providing the dogs are safe when they're together and also have opportunities to be alone, they should be left to sort out their own hierarchy.
When I've introduced a new puppy I've always fed the established dog first, then the puppy, although it's a case of a bowl in each hand and simply putting one bowl down a few seconds before the other. As it happens I've never had to change that, but as I said before I don't have an obvious leader with my 2. The only time it changes is when my friend's Golden Retriever is with me. She doesn't like other dogs near her food and is a slow eater so she is fed first and shut in a different room so she can eat in peace. Once I've shut her in there I feed my 2 as usual.
I often give treats to my 2 at exactly the same time, a treat in each hand. Other times I may choose to give a treat to one first, then the other, it doesn't matter which way round, but that's how it works for me. If the Golden Retriever is with me she just fits in. The order might be as simple as they all sit facing me and I treat left to right. They don't seem to bother about who is sitting where or who gets treated first.
So I think it's all about reading their body language, recognising if they're comfortable with each other or not and also recognising changes, subtle or otherwise, that may happen as your puppy matures, and responding accordingly
A book I turn to a lot is How To Handle Living With Your Dog by Winkie Spiers. It doesn't specifically deal with pack situations and isn't really about training but is about how to live
with your dog successfully by understanding it better. I love it because I've learned a lot about canine body language and that's helped me cope with Louis and his fear aggression problems with other dogs. It's also helped me have a better understanding of how my 2 get on with each other (tolerance levels) and if I see one is very uncomfortable with the actions of the other I can intervene calmly and appropriately and hopefully diffuse a situation, rather than not spotting it and having to react to something that's kicked off. I certainly don't get it right all the time, but I'm understanding more than I used to and hopefully my dogs are benefitting
