RUFUS IS SO CUTE!!!
It is usually best to wait till he's about 12-13 weeks old to estimate his adult weight. You basically double his weight when he's 12-13 weeks and voila!
There is also a puppy weight chart for yorkies:
http://www.yorkiekiss.com/puppyweightchart.htm
According to the chart, he will probably be 4.5 lbs.
Anyway, don't take my word for it. He could be bigger or smaller, but those are all the references I have.
CONGRATS!!!