If you do decide to take the chronological approach, then I think you should definitely focus on key works--in fact, in many cases just chapters of key works. I think it would make sense to choose a history of philosophy as your guide, staying away from anything overly voluminous or idiosyncratic. Blackwell has a one-volume history by Anthony Kenny that looks good. The table of contents references specific philosophical works, which may help you create a manageable, focused itinerary for yourself. Bon voyage!
Having grown tired of reading secondary material in my study of philosophy, I have decided to read primary texts in a chronological, rather than thematic, order. I have started with Plato and have read most of the works I can find online or at my library. Before I move on to Aristotle, I would like your advice. Do you think a chronological approach is a good idea for someone untrained in philosophy? Do you think I should read every work by a given philosopher, or are there 'key' works that serve as their primary contribution to the field? If the latter, are there any lists that you are aware of that state what those key works are?