I’m bin playing this game for a wile now, and the further you come the more obvious the problem with resources is.
9 of 10 things kost steel.
So the produktion off steel needs to be raced up big-time.
Or you need to make it so that more buildings be upgraded by food.
For exempel everything about product and storage of steel should be paid by food.
Maybe in the first you can feel you don’t have enough steel because buildings take a short time to upgrade, but after a bit of level-ups, when building times go over the day in length you will be soon disappointed to have the steel deposits always full between an upgrade and another.
I can only agree about the fact that you will end up at level 20 having 4 mines and 9 farms seems a bit odd, but I think is well thought for the game mechanics.
If you aren’t producing enough iron, then you need to upgrade your mines. I never had a problem that I would not have enough iron, while mines beeing maxed.