Hi and welcome!  Mochi and Kimchee say hi to your furbaby.
 
I have my 2nd Yorkie for almost 2 months now.  A few things when considering for more than one yorkie: 
1) more time involved ino routine care, training, etc.
2) more expenses involved in vet visits, vaccines, treats, etc.
3) they have to be constantly watched at the beginning to make sure they get along
4) they have to have spearately individual play time with you so that they will think they are equally loved 
5) you will get more yokrie kisses 
 
  
Those are the points I can think of, I think other YTers can add more.... 
PS.  I got Mochi when Kimchee was 2 years old.  It took Kimchee 3 weeks to accept Mochi as one of the family members.