A good way to make money:
1) use only normal arrows 2) use auto aim 3) shoot the castle with you're normal arrows and shoot the people when they get close to YOU'RE castle, (kill the catapult last) that way, you get 10 gold per each shot you get on the castle, it might get annoying, or long, but other arrows wont work on it, and you get an average of about 2000 gold, or more, if you continuously hit the opposing castle.
You should really have a restart button, cause every time i kill a civie or have one of my guys die, i have to go to the menu and reload the level again.