Well, if we take a look at the Alloy of Law supplement rule book for the Mistborn adventure game, which Brandon has said that the adventure game and supplements are canon until he contradicts them(he didn't want to give away details that could ruin future books). We see that 1-50 people in the elendel basin are metalborn(either misting or ferring). So assuming there's 5,000,000 people in Elendel, that means about 100,000 are metalborn. Than we divide that by the number of powers available - 32. Now assuming they crop up equally, that means that there's about 3,125 coinshots in the city alone. The supplement book also states that spikeways are regularly made as a cheaper alternative to trains when it comes to remote towns or towns in difficult to reach locations. I'm new to this forum by the way, so I'm not really sure how often people refer to the adventure game rulebooks, but as Brandon has stated their canon until their not at a Q&A, I just kind of roll with that.