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The issue with the constraints of the column happens because Revit tries to keep the bottom of column attached to the top of the structural foundation family. To correct this, you need to open the structural foundation family and redefine that "top", by naming a reference plane at the bottom of the hole as "top". Now the column will respond to the base offset and will lower its base to that plane. See illustration.

In general, this exercise would be a lot easier to do directly in the project. Once you load the structural column family and the structural foundation family (with this modification) in a project, adding more columns and footings is very simple. Create grid lines, and then insert columns and footings using the "At Grids" button. The wire could be done with a railing family, or by copying that family that you created to represent the wire and metal supports.

Making this as a family is complicated. As you have seen, it can be very time consuming. Also, nested structural elements in families do not work as expected in the project.