I would imagine most mobs would be assigned to biomes with closest "zones" to the starting area having the weakest mobs and as you venture further out, you'd come across stronger mobs. I also would think you'd find something like deer, rabbits, and other common animals regardless of difficulty of a given area.
How challenging an NPC/mob is would likely be expressed as how many hit points, how armored (dmg mitigation) they are, and how much power (how many attacks they can potentially make) they have. The exact mechanics of these I don't know so just used some generic terms.
Resources are also likely biome specific so trees and rocks are probably found in most of them. I do recall mention of some resources being not only planet-specific, but region-specific on the planet.
