That Falconreach Idol quest was a really important lesson to me about why we hire professionals with years of training to do voice acting...
The way a character sounds is a really interesting aspect of character design, though it is unnecessary in most written media. For example, Dolores Umbridge (from Harry Potter) has a trapped voice in the films, but no mention of it is made in the stories...
Vaal, Mazurek, and I think Akanthus have their respective laughs (which sound perfect, at least for the first two).
I imagine the Hero's voice (I play as a female) as relatively deep, and slightly breathy, in a way that is not noticeable when delivering angered dialogue-- where it becomes quite strong, even forceful.
For other voices, my opinions are:
Xan has no indoor voice, and would deliver everything from the top of his diaphragm (I mean, he is probably in a constant state of suffocation from all the acrid smoke...)
The NSOD never has an indoor voice, and basically shouts absolutely everything.
Tomix's book 1 voice would be a tenor, though with a whispery, ragged quality behind it (black speech bubbles and all). In book 3 it'd be slightly deeper, containing less emotion, and in general closer to a monotone. He'd also have the accent...
Falwynn would be of a regular pitch, though her voice would raise its pitch as she becomes more excited. There'd possibly be a certain anime protagonist aspect to her voice, as well.
Gaelan's voice would be very soft, even when annoyed.
I'd see Faust as having a very dry, almost humorless tone. Perhaps a drawl.
In comedy quests, of course, it's perfectly viable to imagine the characters with the voices from Rocky Horror.
For some reason, I considered the Azaveyan accent to be more Scandinavian, obviously varying across the continent as a whole. Perhaps if the Magesterium had a rival group, with whom they played a constant game of football with the Azaveyan citizens, it would've seemed more like Poland.