Tips on organising the survey of a large body of literature
If my opinion, a good survey is not a snapshot of what is out there in the literature, but rather is a presentation of the current state of knowledge on a subject (which will necessarily involve some snapshots of what is out there).  This model of knowledge is the novel contribution of the survey.  Your goal, then, is to develop enough expertise in the "lay of the land" to be able to see a pattern that may have never been explicitly enunciated in the literature before.

As such, I recommend the following iterative approach, which has been useful for me in preparing surveys:


Begin with a hypothesis of the structure of knowledge on your topic.
With keyword searching, find lots of articles related to the topic.
Do not read the articles: read just enough to make sure they are actually relevant, and download and organize them into categories based on your hypothesis.
When you've got a big enough pile, skim them to see how your hypothesis is holding up, and adjust it to fit the reality of what you've found.
Repeat from 2, with your adjusted hypothesis, gathering more references, until you find your hypothesis is beginning to stabilize.  Once you've got a stable hypothesis, you are ready to write, and your final organization will reflect the discovery enunciated in your final hypothesis.


A good survey is probably going to be in the 50 - 200 reference range.  If you are finding that you are gathering many more than that, consider whether your subject is too broad and you need to narrow its focus.  It may also be that you have an appropriate focus, but that you are thinking about too many details, and you need to go into less depth in your investigation.