We were going to get a second but wait to do so when Hope turned 1. We really hoped to get a sibling of hers when the breeder mated her mom and dad again.
After doing a lot of reading and asking here, we moved more quickly than that and I have not regretted it even one moment!
After having Hope for just 2 months, we were ready. Hope was 16 weeks when we got Ruby who was 14 weeks. We just added Eden when the "big" girls were 11 and almost 12 months She was 8 months old.
I am fortunate and my lot got along right from the beginning, but for me, adding the second, younger, while the first was younger was MUCH easier.
Hope was high maintenance as a little one. Having a playmate helped with that. It actually allowed us to enjoy her more ourselves.
The two youngest have the most energy so now they run and chase and it allows miss high maintenance to have some time to herself.
Since she turned out to be more independent, it is nice that the other two need me more.
Ours is a nice balance.
Adam was 4 mths when I got Hannah, although there is only 2mths between their ages coz I got her much younger! For me it was realiesing that I dont know any other dog owners and he wouldnt often find a friend his size to play with that made me get another so soon. Although he was already pretty good with his puppy pad training and socialising at this point.
I would say that when you are happy with their house training and have gotten your primary socialisation/training out of the way then you can think about another one. Chihuahuas are so people orientated as well that you dont have the worry like with some breeds that they will bond with each other over you.
Im def glad I got them so close together (and no 3 came at just under a year later!!). As Im out at work for about 13hours 2 nights a week they have company to snuggle up to.