You can certainly use blended meats. Try combining ground beef with ground pork or lamb to produce a richer flavored burger patty.
In relation to portions, I find that a pound of ground meat is going to give you 3 patties. I suggest that you plan on about 1/3 pound per patty.
Divide the meat into twice as many equal parts as the number of patties you are making (about 1/6 of a pound). Do your best to make the portions as equal as possible.