I'd like to add a very simple yet very hard way of increasing the difficulty of the game.
Decrease day time to minimum (10 minute days).
By the time you cut your second tree and because your campfire and forge are running, you'll get at least one wondering horde heading to your location. I think, but I'm not sure, it's because the heatmap scales with day time. Is this correct? Would that mean a 180 minute day server will require 3 times more heat to send screamer/horde?