To get easy money, buy a load of apple orchards(about 30)and make sure they all have labour, a market and about 5 granarys. When all of the granarys are full, sell a load of apples for about 20 gold coins for 5 and keep repeating until you have the desired amout of money. Hope I Helped Happy Gaming ;-)
It's quite simple. This can only work for as many siege engines as you can co-ordinate this with, but, to keep firing rocks even when the siege engine says there are no rocks, order to fire a diseased cow - then cancel before the cow is fired. A rock will be thrown instead, and no cows will be used up either.