A nice concept to incorporate into this mod if it can be done is that all these resources that are provided by all these tile improvements are actually used for something - how about feeding your population? Genius, I know. Remove all food production from all tiles and derive it from the food resources (corn, wheat, etc.) instead. Have buildings which convert the food resources into food to feed the population. City tiles themselves will probably need to produce food the "vanilla" way so that they don't starve right away. That takes care of all of the resources except horses, they were used more for production than food, so maybe each horse resource you have can provide hammer bonuses?