Great post TWW. I would like to add that each dog is different. Some come right in and never miss a beat. It is like they have been a part of the family all along. Others need time to trust. In my experience, the first couple of days, they can be very standoffish and/or very stressed. They just want to be left alone. This can last a couple of weeks but you will begin to see small steps forward. It is not like they will be totally standoffish for six months.
Hell, I had a puppy like this, the breeder had seen this in him and explained the process like this.
At first he will look at you and think "Yuk, it's a girl". A couple of months later, he looks at you and thinks, "Boring, it's a girl". A couple of months later, " I kind of like that girl" A couple of months later, " You are my girl, I love you". Then finally, total love and devotion. I loved that dog with every fiber of my being, yet I could never love him as much as he loved me. That is saying a lot and is very special. Well worth the journey.