When measuring sunlight, keep in mind that, especially in smaller yards, the amount of sun can vary radically at different times of the year, and that you need to plan and plant accordingly.
Our building (vintage Chicago six-flat) spent a small fortune last year re-landscaping (if you can call overgrown yews and lawn grass that doesn't thrive landscaping to begin with) the front yard with a "landscape architect" who came with a personal recommendation from someone in the building. Don't get me started on condo politics, please
This supposed professional visited exactly once in March/April, and then printed up pretty pictures of plants (with no indications of scale) and ordered plants. A significant number died last year because they were simply not suited to the conditions. A significant number died or failed to flower this year for the same reason.
Much of the loss of plants could have been avoided if the so-called professional had simply noticed that one tree in the parkway was a linden, one of the last trees to leaf out, but which then provides a pretty dense shade.
Bottom line, start watching your sunlight now through the fall (it will be approximately the same in the spring, although the effects are a bit different because the sun is moving in a reverse direction). Start reading about days to germination, length of time to production, etc. (all of which is in the Rodale book I mentioned).
I second C2's rec not to just dump topsoil on top of unturned soil. One of the things that happens if you try to do this in smaller beds (even 5 x 12 feet) is that when it rains a lot of the soil just washes away. Part of this is basic physics. Part is because Chicago soils are essentially clay soils, so rain will go through you topsoil, hit soil it can't easily penetrate, and then just run off with your topsoil.
Also everyone's rec of getting a soil test. I also still strongly endorse raised beds because I think they work well with aging knees (or the prevention thereof), troublesome soil conditions, and can really make an attractive addition to a small yard.
Another interesting book to look at is Rosalind Creasey's "Edible Landscaping."