I may not be the best person to answer this because I love my Yorkies to pieces! However, I will give you my opinion. I have two females right now.
Strong headed, yes. Both of mine can be very stubborn when they want to be. But so can their momma so I have dealt with it.
I do think behaviors have a lot to do with how they have been raised. I think if you let them have those types of behaviors then they will use them. I do not have an aggressive problem with either of my girls. They will bark if you ring the door bell but then want to jump in your lap and give you lots of Yorkie Kisses.
Potty training was not an issue for either of my girls. I think the number one thing is consistency. I felt like Rosie trained very easily and Mikki was already potty trained when I got her. With that said, I have a friend with a male that has a lot harder time than I did. I don't know if it is the difference in a male or female or what.
Hope that helps! Good luck with your decision!!