You are still getting up to speed on the tradition, so time spent rereading the classics is time well spent. Book length treatments of persons, issues, concepts, or whatever. These will help to put your topic into a context. This is much more technical, but you might as well dive in now as later. Browsing in the 100s, in both Reference and the main stacks.
Serendipity is a wonderful thing.
The On-line Catalog. The Philosopher's Index. This includes journals, articles from anthologies, and book reviews. The bibliographies and notes of previously identified sources.