If I Adopt A Older Papillon, What Will I Need For It/ Need To Do?

It says that she is potty trained, but I do not have a doggy door. Would it be hard to retrain her to stand at the door?
I heard you have to brush their teeth. Do you buy a regular tooth brush, and what do you brush them with?
Anything else I would need to do/ need to buy?
I already have another dog, so I have food/ water dishes, etc.http://www.petfinder.com/petnote/display…