If the railing is the open kind, you may be able to hang pots from that, the sunniest spot you have. I can't tell if you were aiming for ornamental house plants, flowering annuals, or more in the veggie/herb realm?
Julie's pic looks like all that is going on in only a few sq ft of space.
It might seem counter-intuitive, but I've learned from my covered porch that lower = more light. Plants on a stand or tablewill be in the shade much more of the time. If there's a sliding glass door, and you won't go out there when it's cold out, sitting just inside the glass should be a good spot for winter for plants that were just on the other side for summer.
