What texts do I use? Luckily for me, and my wallet, most of the texts my character is based on are in the public domain, and are thus available online. Not the best solution, but I'm a college student and my money goes to food and school books, in that order. There are a few books that I do have, however.
Our Troth Vol. 1 and 2 by members of The Troth, compiled by Kveldulf Gundarsson. This one is a big reference for the religion of Asatru, which Brendan is based on. It has a rough overview of history, the gods, the other supernatural creatures, also information about holy days, blot, sumbel, etc. Really a huge resource. The contributing authors give plenty of citations for their work and they are all fairly well respected in the Asatru community. EDIT: Disclaimer: As with any text compiled from smaller articles by multiple authors, many of the citations are for these smaller works and it's not till the end of the book that we see the actual books most of this is based on.
Futhark: A handbook of rune magic by Edred Thorsson.
Essential Asatru by Diana L. Paxon. A rough overview, not quite as detailed as Our Troth but with some details that the bigger books lack.
The Poetic Edda translated by Lee Hollander. Nicknamed by some "The King James Edda", it stays true to the original flow of the language by using quite a few words not normally seen by your everyday American.
Edda by Snorri Sturluson
The rest of my texts are available online.
German 1500: Germanic Myths, Legends, and Sagas Huge resource, as the class is pretty much everything that Brendan is based on. There are also links to pretty much every other important text from the time period on that site.
Note: Some of these, I have not had time to read yet, and are listed for my reference. I am in college, time is short, sue me.
The Sagas of Olaf Tryggvason and of Harald The Tyrant (Harald Haardraade) e-text from Project Gutenburg
Heimskringla, or the Chronicle of the Kings of Norway by Snorri Sturluson also from Project Gutenburg
The story of Burnt Njal
The Story of the Volsungs, (Volsunga Saga)
Eirik the Red's Saga
The Troth's Book List has several others that I refuse to go and re-link. Go, Read, Learn.
Some specific terms I've seen conflict with, either because they are used differently elsewhere or just aren't used at all:
Wight - From Our Troth - any sort of conscious being. You, Odin, and the Thing that Goes Bump in your yard at night, can all be called "wights". Among heathens today, the word is most often applied to beings in the class of the Thing that Goes Bump (as in "What the Hel is that wight out there?") or used as a wide generalization ("all holy wights" means gods, goddesses, ghosts, land-wights, humans, and well meaning etins and other creatures). Similar in many ways to the Japanese concept of kami. (Old Norse vættr, Anglo-Saxon wiht, Modern German Wicht)
Incidentally, searching for "Wicht" in a german dictionary and clicking on the explanation of "wight" gets you this answer. Note that as far back as Chaucer, "wight" was used in the sense of "supernatural creature", among other uses.
German "fairies" - I've never encountered the term "fairy" in my research. Grimm's Tales are Kinder und Hausmarchen. This is often translated as "Grimm's Fairytales" but a more direct translation is "Children and Household Tales", stemming from their origin and purpose in 19th century Germany. Most of them do not involve "fairies", but regular people, often (but not exclusively) girls, who get into difficult situations.
Fairies in Germanic tales are referred to by many names, often "changling" when dealing with them stealing children, which they liked to do before the child was baptised. Also "hill-woman" or "underground woman", "the underground people" or "thickheads" when dealing with dwarves. Nixies were known, as were changlings called "killcrops".
Our Troth's entry on wights will have to wait. I'll retell it later.