One of the things about a townhouse is you dont have a really private 'yard' most likely. That means the sort of things you might store in a fenced private backyard of a house, are problematic in your situation. I'd sell all but one of the lawn-mowers and get rid of the wood except the discrete piece you say is under the porch and not visible. I'd think of replacing that too with some sort of paving stone.
The gas, just left out in the sun isnt very safe. It's the one that may be a code violation.
You may want to consider one of the smaller rubber-maid storage sheds. They have several designs of small ones that seem to be workable for your situation. Make sure it's vented if storing gasoline or a lawnmower with gasoline in it.