The survey is valid for six months, as per DCRA requirements, but it can work as long as it is reproduced in the drawings showing exactly what is on the land.
Area of the foot print of the covered property (all that is under a roof, it doesn’t matter if it is open) versus the area of the land, and the difference is the uncovered area.
New building codes/green space have nothing to do with FAR (floor area ratio) regulations.
You don’t earn anything by doing anything such as rain gardens or any other feature. It is an absolute number not a point system.
Open pergola is an uncovered area.
The rules are not about green space. The rules are about covered versus uncovered, paved areas that are not under a roof are as uncovered as green areas that are not under a roof.
There are differences in zoning, there are lots that have zero lot lines (houses that share a party wall) some other lots are semi attached. Some other lots have 100% coverage, all will depend on your zoning code.
Your zoning code, your zoning map, and the survey have the keys to what you can cover, or what you must left uncovered. It’s possible that the house next door is zoned differently, one must look in the zoning map and see where the boundaries of a particular zoning code lie.
DC Zoning Maps: http://maps.dcoz.dc.gov (here you enter your address and you will find under which zoning code your property is located)
Your questions about set backs (distances from the property lines to the exterior walls of the buildings) should be asked to a zoning officer at DCRA, as well as the questions about how much of your land can you cover with a roofed structure)
Zoning brochure: http://dcoz.dc.gov/dcoz_brochure_013111.pdf