They chose to keep details a bit unclear to leave room for "discovery" later on. But practically speaking, they may have done that to give themselves some wiggle room to adjust as needed as well.

All populations right now are NPCs. PCs will simply replace NPCs when they enter into the world, so that number is fixed at launch, but it can and will change thereafter.

The maps you are seeing are NOT for alpha. These are the maps that will be played on at launch. Alpha and Beta will be played on a separate map specifically for test purposes.