Here is a strategy guide for gaining as much might as possible when having 2 cities.
Main city (city 1): keep all the troops in this city. Destroy all the farms and build/produce only wood, stone and ore.
Second city: build farms as much as possible and when you think you are generating enough food, start building wood, stone, ore buildings. Train Tier 3 troops here and from time to time, reassign them to city1 so the food upkeep will stay very low.
So, send from city1 to city2 wood, stone and ore, build troops.
Send from city2 to city1 food, build troops.
The same thing from the second city can be done with a third city.
A few tips for your second city: don’t build Academy, Sage’s Tower, Embassy. Instead of these three, build three barracks.
I mostly build tier3 troops because I rarely have to check and send resources from a city to another, maybe once or twice a day.