Andromeda Galaxy & Milkyway Galaxy?

Both are very big indeed, and you are right to say that Andromeda is significantly larger. Your numbers and insights all seem to be correct, except Milky Way being freakish, normal is a better word.The largest galaxies that we know of are giant elliptical galaxies in the centres of clusters of galaxies. They are sometimes called cD galaxies (for giant diffuse galaxies) or BCGs (for brightest cluster galaxies). These galaxies are about 10 times more luminous that a typical galaxy (like the Milky Way) and about 100 times more mive. They can have diameters of more than 6 million light years (compare to about 100 thousand light years for the Milky Way). A good example is the central galaxy in the cluster Abell 2029.