[b] Provided that at least some spells are cast via saying an incantation and sundry other requirements:[/b] Incantations are not how magic is done as I feel that would make it come from some otherworldly source, however magic does follow a glyph/rune system (Sana does spelling I am awful at it) where magic flows along channels and as it does it changes properties, our version of magic is more like modern day chemistry, if one uses x on x than you get y but if x passes through x you can get a x^2 effect but you are using a limited amount of your mental endurance, similar to a mana system but think of it as a different section of the brain (their brains look the same its just more active) and just like muscles the more you use magic the easier you can do it and the stronger it can become....but some can be more talented and genetically inclined to reach levels that others could not.

[b]What happens if someone misspeaks the incantation?[/b]  In the same sense of things, if you try to use a spell and you dont form the glyph properly, well as I mentioned this is similar to chemistry and based on the type of spell the negative effects vary based upon the scope and purpose of a spell
[b]What if some of the accouterments fail but the incantation and intention are correct?[/b] In this I believe the term fizzle best sums it up, as you lacked the ability to gather enough "magic" from yourself and your surroundings to produce the effect you wanted, so depending on what you where doing it could either produce a weak or twisted version of the spell or it may just leave you tired and looking like an idiot

[b]How are new spells created?[/b] New spells are formed through experimentation, using the fundamental information of older spells and how things flow the most astute researchers (They don't need to be mages to come up with magic theory) can produce results that can be trialed till perfected, or proven out of reach (But hey technology grows with need so hell with the resources and time anything is really possible, but I will say that matters of reanimation are not only taboo but generally pointless as 
[b]Is there a clear translation from intended action to incantation/actions[/b]? Though Glyphs are quick or instant for the most skilled of magus the majority project a literal guide based on memory this in and of itself does take some basic understanding of the magic but once they get a feel for this its not something that the skilled suffer with. In addition Runes and enchanted weapons while rare exist, as everyone has magic potential these enchanted weapons and armor work off of their raw magic and gives it form but like mentioned before this will still tire them, but it makes many things more practical (or more dangerous depending on how you look at it)
 [b]Does it require some control over magic, or is it able to be performed by any old luddite?[/b] I think I answered this above, but magic is easier to control here but at the same time requires practice to truly use
WHERE DOES IT COME FROM
[u] Is it biological energy made from ATP and pushed into some hitherto-unknown magic-organ? Or is it something like direct matter-energy conversion, and a person loses weight when casting, or is it drawn from ambient matter/energy, or pulled from other theoretical universes parallel to our own? [my understanding of quantum theory is not excellent, I apologize] Can someone do more work than the energy present in their body is theoretically capable of doing, according to modern understanding of biology/quantum physics?  [/u]
It works on all three principals but the theoretical universes is a spoiler so don't work on that one much 
This is also assuming that spells can be manipulated by magical aptitude, or magic can also be done without incantation

As for the dark suns, I believe that in and of itself would be a form of spell play to force drain an area of its natural magic or even make magic unstable (This sounds like a viable explanation for a counter spell or antimagic zone in the world that we are trying to create) this however is mad taboo.