yay my 1st post here,and wish you guys the best of luck with War for the Overworld,its an epic project(wish i could help in some way)
I think that iron ore should one of the resources in the game,but not a plentiful resources like gold and manna,this would make gems a little less useful.Armor,weapons some doors and some traps should need iron to make(or everything).The ore could be obtained by mining away rock,one unit per a "block" of rock,or by melting down goodies' armor and weapons
my English can be a little weird,sorry for that