I just need clarification:

Is the Metal Alloy the only piece of Raven's armor you get in Chapter IV? The Prima guide says the Elven Notes can be found in the Crypt in the Field, but I could not find them. I looked everywhere, and even found (and killed) the giant centuar (not actual name) deep in the crypt.

Dont worry, is the only part. In chapter V you will found someone (depending if you are neutral, go with the scoiatael or with the order) who actually tells you about the rest of the parts and how to make the complete armor :)

There's also a second metal alloy in Chp 5, so even if you miss out on the one in Chp 4, you aren't locked out of the quest. I'm honestly not sure why they even bothered to put that first alloy in the game at all.

Probably to totally throw the player off just for fun.

Is it worth it to buy the Steel Sword from the Blacksmith's Son in Murky Waters if I don't expect to complete "Won't Hurt a Bit" (Dentist's quest from Chapter III)?

On a semi-related note, the Lakeside music is absolutely beautiful...

I figure the Lady of the Lake's gift is decent, so I'd rather upgrade the Steel Sword. I chose to ally with the Scoia'tel, so I expect to be fighting humans in the endgame.

Aww crap. I don't have a bestiary entry for dogs or wolves, and currently the beast fang is the only item I am missing for the Dentist's quest besides the Famous Fighter's Tooth. Can I buy the Book of Animals in Chapter 5?

You do not need the book to collect Beast Fangs. But if you have already finished Act IV (where wolves are abundant), you won't have an opportunity to collect one until nearly the end of Act V.

I got some Beast Fangs. I'm right at the end of Act IV. All I have to do is go talk to the Lady at the Lake about Berengar and then the final quest of the Act starts.

Also, about Berengar:

1) He's kind of an @ssh*le. Kinda arrogant for being stuck in a crypt. Yeah, I killed the Professor, and you're stuck in a friggin crypt. Who's the badass, again? I might spare him anyway, because he will help me later.
2) He looks like Rick's best friend in The Walking Dead.

I completed Chapter 4, and I just played Ring Around the Sarcophagus with Princess Adda/Striga, and now I wish to finish the Dentist's quest. But I have not encountered the Famous Fistfighter, probably because I didn't get the Fighter quest. I take it he won't appear without the quest?