The Final Empire By Brandon Sanderson
One note on the numbers of mistings, its actually considerably higher, the number of 1 in 10k is for mixed breed skaa. Nobles have have a much higher percentage of mistings and the number of mistborn (from memory 1 in 10k skaa allomancers is mistborn, but I can't remember where I heard that) is also comparatively higher. Other than that I would agree with a figure around 500million for population of the final empire.
The Final Empire by Brandon Sanderson