Just thought id add my input to the orc/ogre/whatever thingy. Perhaps the orc could be a sub-race of elf? Considering the elves are a peaceful, quite dormant race and the Simians are a very active, experimental race, I dont see why the Simians wouldnt try some genetic experimentation nonsense and fail miserably and create an orc thing. Ofcourse, one wouldnt be enough for a whole race, so for story-sake, perhaps they had a massive lab filled with these experiments, and one escaped and "somehow" released all of its friends and they bred in the wilds and caves.

I know this is very cliche, but eh. I dont see how an orc would come to exist from a reptillian, but thats just me

This looks great

Expanding on the idea of protecting the world, perhaps in a plot you can only destroy grass, rock and what you place, That way the original owner can put stuff in there to designate or whatever, but the player cant take that down. Also, perhaps within a, say, 16 or so block boundary around a town or stronghold noone can build or destroy blocks. This could help maintain the look and feel of the world.