Ryzom

Has anyone already created or know of in existence a spreadsheet showing the different NPCs and their HP Count, Damage Output?

I'm trying to make a decent single player dungeon but I am greatly concerned about the difficulty.

Put every NPC down in an empty map and see for yourself? It doesn't take that long. Just HP count and damage output of the individual mobs doesn't tell you much anyways, there's a lot more factors that determine difficulty. You'll likely have to test your map as a whole a few dozen times to get the difficulty right.