I used ALL 3! Started out crate training....did pad training esp. for at night all the while taking my girls out side... My ultimate goal was to teach them to potty outside..but the pads were for ...just in case I wasn't on my toes and they had to go....I'd just move the pads closer and closer to the door I took them out to potty.. And I always used the SAME door every time when we went outside...so eventually I would see them go to the door...and knew it was Potty time! Good luck..yorkies can take quite a bit longer to train than a lot of other breeds.

I also used the word POTTY when they were going...so when I say Potty..they know what I'm talking about!
I don't have a doggy door...so I ALWAYS go out with my girls...but I can see why you would be worried about your little one going out alone!