The information and bonuses listed below are for all resource fields the exact same, e.g. 40 lumber mills. When you start off on the server you should mix fields because you will need mixed resources at the start, but when you start capturing Historic Cities make all the resource fields the exact same in each city. This optimises and maximises what you can produce. Lumber is probably the best resource to produce overall. It sell fairly high at the market and is used the most for overall troop building. Stone is worthless and iron just takes up too much population. Food can be another option to produce instead of lumber because farms use the least population meaning you can have less cottages, however food is always been eaten so with a large army you will probably still always be in negative production. Remember the higher level your resource fields go up the more population you need.