First off, welcome to AW!
Hmm... lots of questions... let's see if MHOs can help in any way...
I am writing a fantasy series of ten books and have reversals at key points which I intend to deliver as "set pieces."
Is it too improbable to write an orchestral scene and describe key movements when no reader can imagine the exact lay being played on specifically-pitched instruments?
Do you have a stage or screenplay background? Because you seem to be thinking visually/cinematically. Novels are a somewhat different beast. Is it essential that the reader "hear" the precise musical score you have envisioned, or is enough to know "the music swelled in bold, triumphant notes" or "a lone piccolo pierced the still air" (bad examples, but hopefully they get the idea cross)? You're going to have trouble if you get too "musicy" (not a word, I know, squiggly line) and technical trying to describe things, like someone giving a castle description with precise measurements, directions, and stone brick counts. Which is more likely to draw a reader in: ten pages of architectural notes, or descriptions of how the castle "loomed like a black vulture on the cliffs above the valley" (another bad example)? Your vision of that castle may not be precisely my vision of that castle, but it's good enough for the story, and if more is needed, more can be worked in. At no point have I ever read a tale in which the precise, detailed architecture was absolutely vital for my enjoyment and understanding of a story.
If it's still important to you, I've seen some authors include appendices with musical scores for in-book music. Describe it as best you can in the text without derailing the tale for the symphony seating chart, and let enthusiasts look to the back for more details.
That is the first part of the question.
The other part is, that the scene becomes a set piece because, the Sea Folk Empress; in a show of disdain for the enemy; dismissed their entire military machine and then promised to show them how to execute a signal defeat in style.
First off, nitpick: you want commas, not semicolons, in that sentence. And did she dismiss the enemy's military machine, or her own? If it's the former, she already has defeated them, if they acquiesced to her demands. (Or they're just plain too stupid to win.) So the rest is needless humiliation, though it may fit her personality to not only win, but utterly disgrace and demoralize the losers. If it's the latter, she'd be showing off - though one wonders why she employs a military machine if she's that powerful.
On the day in question, she rewrote all of the rules and mounted the crows nest alone on her flagship and visible to the appropriate ranks of her fleet, gave the signals and a crash of cymbals and rataplan of drums beat out a dramatic upswell, while the climbing clicking of castanets, merged with each layer of swelling percussion and accompanying instruments,
and when they climaxed!
The first wave of murderous military insects were released!
Now, see, I can visualize the musical rise here without knowing the exact notes. Seems a trifle overwrought, as a single-sentence excerpt, and I don't know what the "rewrote all the rules" means (what rules? why?), nor am I sure why she goes for the cinematic music - except again, if this is part of a grandstanding piece of showmanship, psychologically driving home her power to the helpless victims. (If you want more critique, you'll have to get up to 50 posts and try your luck in the SYW forums.)
Also, could the Sea Folk Empress be considered a perfect villain if she liked to sing and physically execute the arrangements specific to a musical number in an old movie?
Um... not quite sure what the question is. What makes her a villain is her motivations and her actions, not using musical arrangements in victories. Good guys in musicals sang and danced to victory, too. She would be a perfectly grandstanding, showy villain, IMHO - but that may fit her personality, that she likes to make the biggest show of defeating her enemies as possible. Again, I don't know your story or your world. It may work, or it may stand out like a sore thumb. (And I'm hoping you're not intending to refer to real-world musicals. For one thing, unless you're doing alt-modern or alt-near-history, our cinematic heritage would be unknown to them, and referencing such things would send your readers' suspension of disbelief crashing into the waves faster than a seagull strike. For another, most known musicals are still protected property, I believe; merely mentioning them tends to be okay, but if you're copying their "set pieces" in text, you're wandering onto very thin ice.)
And, I ask of all here,
Would you suggest a good way to derive another name for the overused word, seafolk?
I have tried different languages and their word combinations, but no good.
You could make up your own; there's no reason you have to be married to our world's languages. Try taking a few adjectives or words that describe your merfolk and mix up the letters until you get sounds you like... though if they are essentially merfolk, you might be better off just calling them merfolk. (Refer to the "calling rabbits smeerps" problem.)
Good luck!
