I am going to play the devil's advocate
I have a chi named Mister he is just around 4 pounds. He has his therpay dog tags and is fabulous with nursing homes and the VA hospital we go to.
HOWEVER....he can be nasty and I will be the first to say so. Mister will bite you when I am holding him
They are around the clock care when they are itty bitty.
And still almost being 3 yrs old he still has to go out much more often then your "average" size dog. Also for a tip chihuahuas have been know to live up to 25 yrs. So its a long time commitment.
Dont get me wrong I love Mister to death heck I bought him food instead of myself. But with the good there is some bad.
Chi's can revert into their typical character traits if the training isnt consistant. This I have learned the hard way.
As for the others on here with their chi's I cant speak for them but Mister is a one person(me) kinda dog. He likes other people but is a true die hard mommas boy.

Before I got Mister I did some heavy duty research on the breed I suggest you do the same. ALso if you CAN rescue please do but if not find a GOOD breeder. Call your AG and BBB to make sure the breeder has never had any "bad" reports. Besides that I wish you luck