Very smart of you considering the grooming factor, which you would need to do with the Maltese, too.
Chihuahuas are know for their small bladders, but the ones I take care of all have pretty good potty skills. They are also all on the timid side and the one still hasn't warmed up entirely to her owner's husband I am told. You'll find this with a lot of lap dogs, though. They are primped and pampered and don't get "out" much and socialized. Most of the people I know that have them have them trained to go on puppy pads (or Depends actually, much cheaper). They live a long time, too.
I'd go for it. [img]/forums/images/icons/laugh.gif[/img]