Hi
I think the best one is Stronghold and Stronghold Crusader. Crusader is basically Stronghold in Arabian atmosphere with more war-like themes. If you are looking for Castle building economical challenge then start with basic Stronghold - there were more predefined economical missions in that one. Also in both games you have Free Build mode where you can build your own castle without any enemy forces and bandits encounter.

@j39hsieh
But bunnies are dangerous - they can eat your crops if you will not control them. So sometimes you need to just butcher them with your soldiers. Actually in one mission if you will not kill bunnies you will never win :D