Congratulations on your new puppy! I hope you did some research ahead of time on the health concerns and what not, but here is a couple links I found off another thread in here.
But anyways one of the main concerns in chihuahua's is low blood sugar, called Hypoglycaemia, which is comain in chihuahua's because of their size. But you can easily prevent this by making sure he/she is eating enough daily, also drinking. Although it can happen unexspectedly, even if she/he is eating fine. So i'd suggest researching that if you havent already. Because you need to know all the symptoms of it (I think its in one of the links below) so you can take him/her to the vet right away. Also, its good to have honey or corn surup on hand incase she/he isnt eating enough that paticular day, just give him/her a dab on ur fingure once a day. I got Nutri-cal from the vets, some people just use honey or corn surup -- but Nutri-cal is the best.
All your other questions should be answerd here: :wave:
http://www.canismajor.com/dog/tpuppy.html
http://www.chidolls.com/puppycare.html