Thirded on the slow intros...
In my experience it's way easier to introduce a new puppy, since most dogs are fairly tolerant of young dogs... adults are a different story.
When I brought Luka home (adult AND intact) I was very careful w/intros... he was crated in the living room at first and he sort of became "part of the furniture" after a few days. I then moved his crate in the spare room w/the others and everybody interacted while I crated/rotated... when Luka was out of the crate the others weren't, and vice versa.
I introduced everyone seperately on my porch (w/Luka on-leash) since I wasn't able to walk them together on neutral territory (no friend to help
), and the only one who took offense was Bee... she absolutely goes into hysterics around Luka, so I still keep them apart now.
I was very careful about toys, treats, and "personal space" (for lack of a better word)... I did not allow Luka to take over anyones individual favorite pillow/blanket, toy, or favorite spot on the couch.
Luka didn't know ANY commands when he first got here, but he quickly learned by watching me interact w/the others - no treats unless you sit quietly, no barreling out of an open door, etc.
I bought new toys for playing in the yard, so there wouldn't be any issues about the "new guy taking over" favorite balls or Wubbas... I only give high-value treats like bully sticks and bones while everyone is in a seperate space or crated. The same goes for feeding time.
I make sure to spend time w/each dog individually as well... because I was thinking that, if MY mother suddenly brought home another kid and moved him/her into my room, I might be a little put out and/or jealous if she expected me to share all my stuff...
So far, so good - we have established a great daily routine, and it's working well.