Building the Steel Mill is going to test your resource strain, but this is a necessary step in order to reach any unit requiring Steel in order to work with. You're going to need to bite the bullet and figure out a good way of getting* 7,200 Iron while building your Concrete.
Once you have a Steel Mill, keep it running as much as you can, because it is crucial to build yourself that tank battalion you always wanted. Not only that, but to keep said tanks running and out of repair, you're going to need lots of Steel.
To maximize production, place your buildings where visitors (Friends) will see them immediately when they open your world. This makes its easy for them to help you.
After the 1.5 Patch, you can now upgrade Steel Mills for a higher Steel output.
Building 7 Large Warehouses would be one way to attain the amount of resources required and assisting (14 times for regular Iron Mines) your friends for the rest of the iron required. Or simply raiding would do too.