Some of us are going to try out a 3 castles system, and I invite you to do the same.
The three castles system starts with one main Castle, which will be your fighting Castle. There will be a second castle which will provide troops to Garrison inside the main Castle and improve your defense. It will also contain lumber yards and eventually iron mines and Silver Mines . In short, it will produce every resource except food . The third Castle will be a farm. It will have minimal troops and produce mainly food.
The main castle is where we will spend most of our time and energy. It will be well-rounded, with both attack and defense abilities enhanced as much as possible. Outbuildings will contain as many hospitals and military tents as possible.
The reinforcement castle will focus on defense capabilities. Troops and airship will garrison in the main castle. I recommend not training any troops except Lv1 artillery until you can get some lv 3 or 4. (You will need the Lv1 to gather. )
The reinforcement castle will produce very little food because troops will eat it, even if they are garrisoned.
Instead of farms, hospitals and LumberYards will be the majority of the outbuildings.
The farm castle will have only enough troops to go gathering. I find Lv1 artillery are the most efficient gatherers, with the least upkeep. It will have mainly farms, and it will produce and store food. The trick to this is to make sure your upkeep is less than your production.
That is what I plan to do. You may want to tweak the castles to your own preferences