i am sure you are going to get lots of good pointers so i will just mention a few
1.) What should I expect to be my biggest challenges in going from 1 to 2? (I know the double cost - vet care, pup pads, etc..but what else?)
my biggest challenge was i noticed that when i brought in a younger puppy, my older ones regressed a bit on their potty training and have more accidents. also i would not expect them to be best friends right away. it might take a week, two weeks, one month, etc but do not give up! violet should come around eventually
2.) Can anyone recommend good reading for how to best introduce and incorporate a new one into our family? (links to threads here, or other things?)
i am not sure how to answer on this one because my new additions have pretty much hit the floor running, playing, having a grand old time, etc. and my older kids are the sweetest furbabies ever and are always excited to meet another brother or sister
3.) What do you feel are the greatest advantages of having two vs. one?
IMO, they entertain one another and you get more chances for "you" time
and they just seem so much happier having siblings and that counts for a lot with me!