Print(-ish)

Well, your best bet is to read one of the Greyhawk sourcebooks that covers their deities. The Living Greyhawk Gazetteer is the most recent, but the original World of Greyhawk setting boxed set just became available in PDF from dndclassics.com. The later From The Ashes boxed set, the Greyhawk Adventures hardback, and the Player's Guide to Greyhawk that are also available in PDF there also have deity information in them but it's largely identical information.

The Greyhawk gods have been developed and rehashed a lot over time, especially in Dragon magazine/Polyhedron/Living Greyhawk Journal articles and the like and there may be inconsistencies (especially in 4e-5e once they started mashing the deities up together into a generic "D&D Pantheon").

Web

Canonfire is the most respected Oerth Web site, and they have a wiki of the gods with more information that does some sourcing of where specific pieces of information are from. The content there is intended to all be canon and not sourced from fan writeups. There's also a free guide to the GH gods on the now-hidden Living Greyhawk site.

Dragons?

There are some dragon deities, but in Greyhawk there's no such thing as "the gods and dragons" like that's some kind of pantheon; dragons are just big critters on Oerth. In later editions Bahamut and Tiamat got promoted into the "Generic D&D Pantheon" but that's not so in Greyhawk proper. There are major dragons of GH named in various places - like here's a thread that mentions some Draconomicon references to major GH dragons - but they are not spoken of in the same way as even the least of deities. There's also a Canonfire list of known dragons and they're pretty rare.

Yes, and easily found

Go to the White Wolf Wikia, and check the respective category.

The Ventrue Chronicle I didn't read myself, but it seems so from the description that it's the thing you need, providing some plot for Dark Ages: Vampire.

You may get it at DiveThruRPG for 12$ as PDF -- you probably can't afford to wait for the delivery of the paper version if you only have 4 days! The advantage is that this book actually has 3 stories, one for the Dark Ages, one for Victorian Age, and one for the Final Nights.

Dark Ages: British Isles is another book, which may be bought here. However, it has all 4 lines of supernaturals together, so I hope you know them all if you gonna play it. If you get it as PDF, don't forget to download Dark Ages: British Isles Casualties to see the cut content with more details.

Also if you want to learn the setting, you better buy other books from the series than a book on history, because the former will get you more useful information for actual play.