All the valar come in pairs, with three exceptions: Ulmo, who chose to live alone, Nienna, and Melkor. It is stated that Nienna is sorrowful and patient, and weeps for the wounds of the world. Could it possibly be that Melkor is her lost love? That would make her sorrow even more poignant. Her patience seems infinite, also when we remember that Melkor actually wanted Varda for a spouse, but she rejected him. So Nienna can't do anything but weep.
When Thingol heard about the massacre of his kin (the Teleri) by the Noldor, he banned the speaking of their language (Quenya) throughout Beleriand. This meant that the Noldor (whom he no longer trusted) had to speak in a language he and his people could understand, or risk being shunned. It also meant that, while he could not demand that the Noldor get rid of the swords that had killed his kin (since they were needed in the war against Morgoth), he could still punish them by banning the language in which the orders to kill the Teleri were given.
Being a scholar of languages himself, Tolkien also knew the implications of this punishment. It was practically a death sentence to any attempt at exporting or preserving of Noldorin culture in Beleriand as the forced use of Sindarin would, without noticing it, gradually lead to an adoption of the culture of the Teleri. This is reflected by the time of the Third Age, when Sindarin is the high language of Middle Earth, with almost all locations having Sindar names; whereas Quenya, the language of the Noldor, is an isolated tongue known by few people.
Meta-example: The Silmarillion itself was compiled from fifty years of Tolkien's manuscripts, layer upon layer of retellings, many of which were not consistent with one another in detail and often in fundamentals... just like different versions of real-world mythology.
Or even real-world history.
The elves are described dwelling far beyond the sea, on the other side of impassable mountains, beneath the earth in elaborate underground palaces, and in the deep, enchanted forests. In other words, in exactly the places where the Celts used to believe The Fair Folk to dwell. This is most definitely not a coincidence, but a deliberate attempt to tie The Silmarillion to the real world mythology.
The three elvish ambassadors to Valinor seems to have a root in mythology and folklore.
Ingwë, the leader of the Vanyar, is an equivalent of Ingwaz or Frøy. In norse mythology the elves live with him in Alfheimr. The vanyar live with Ingwë in Elvenhome, and hey is there a nominal resemblance between the Vanyar and the Vanir (the people of Frøy).
Finwë was called Finn in the early drafts. Wayland the smith is the son of the Finn king in the Norse poem, and is called "Visi alfa" (elven lord). The Noldor are master smiths, as Wayland was.
Elwë has a name that rings almost like "Elf". His people, the Sindar, seems to be the most traditionally "elvish" elves in the mythology. And like the woodland elves, they prefer twilight and dusk, being called the Grey Elves because of this.
Not sure if this was intentional on Tolkien's part or not, but while Morgoth is Big Bad for the overall story, each of the three "Great Tales" which form the most significant arcs of the mythology features a significant role from one of his three chief lieutenants — Sauron in "Beren and Lúthien", Glaurung in "The Children of Húrin", and Gothmog in "The Fall of Gondolin".
Which characters get the primary focus is something that changes throughout The Silmarillion — first the Valar, then the elves, then men, and finally at the end of "Of the Rings of Power", the hobbits. This reflects Middle-Earth's gradual transformation from a purely mythological world inhabited by embodied elemental forces into a a more mundane world like out own (or possibly our own altogether, if some of Tolkien's Literary Agent Hypothesis comments are to be taken seriously).
It is mentioned that Elrond kept and compiled the stories of the Elves in Middle-Earth in Rivendell, and that Bilbo translated works from Elvish to the Common Tongue while he was in Rivendell. Presumably, The Silmarillion was written by Elrond, translated into the Common Tongue by Bilbo, and then translated into English by Tolkien. That would explain why it is told from an Elvish point of view, though with a very generous regard for select humans.
In the The Lord of the Rings when the Fellowship is formed Elrond tells them (with the exception of Frodo, who is charged to carry the Ring) to swear no oaths to see the quest through to the end. When Gimli insists, Elrond again cautions against it, saying that there is no way of knowing what they're getting into and it's better not to trap yourself in an oath you may not be able to follow through with. Elrond isn't just being paranoid. He knows better than anyone in the room how an oath can backfire. He was raised for part of his childhood by Maglor, one of the Sons of Fëanor (The Fëanorians being pretty much the ultimate cautionary tale in NEVER SWEARING AN OATH or just acting without thinking in general). He saw first hand what the Fëanorian Oath compelled the Sons of Fëanor to do and how it ultimately destroyed them.
'This is my last word,' said Elrond. 'The Ring-Bearer is setting out on the Quest of Mount Doom. On him alone is any charge laid... The others go with him as free companions, to help him on his way. You may tarry, or come back, or turn aside into other paths, as chance allows. The further you go, the less easy will it be to withdraw; yet no oath or bond is laid on you to go further than you will. For you do not yet know the strength of your hearts, and you cannot foresee what each may meet upon the road.'
'Faithless is he that says farewell when the road darkens,' said Gimli.
'Maybe,' said Elrond, 'but let him not vow to walk in the dark, who has not seen the nightfall.'
'Yet sworn word may strengthen quaking heart,' said Gimli.
'Or break it,' said Elrond. 'Look not too far ahead! But go now with good hearts!'
This also leans into the fridge horror part, during Sauron's stay with the Númenóreans he tells them about the divine lord Melkor and all his wonders and a lot of them end up believing him. Why? Because Melkor hasn't gone by that name since the beginning of the first age, and hundreds of years have went by since then, where the somewhat younger Númenóreans might have only heard his tale through the name Morgoth.
It's more likely that Sauron called his master by his original name because of the meaning. Melkor, meaning He Who Arises In Might — awesome. Morgoth, meaning The Dark Enemy Of The World — not so much. It is as if some dark cultist would introduce Satan as "Lord of Lies" or something like that instead of "Lightbearer". Of course, some people fall for the more sinister name, but if you want to go for numbers, pick the one that sounds more appealing.
There is no indication that they were "warping reality", nor that the Valar couldn't have defeated them if they wanted to — nor even that they were afraid, concerned, or anything else.
Actually it's mentioned that one reason Morgoth feared Turin was because he had the potential to grow to such power that he could break free of Morgoth's curse. Turin was just an Edain... the Númenóreans were their empowered descendants and they were at the height of their power so there's actually a good chance that the Númenórean race at this point could defy the 'fate' decreed by the Valar for the world and impose their decision on it. Sure you could argue that the Valar didn't act directly against Númenor for fears of collateral damage... until you realize that Manwë invoking Ilúvatar caused just as much collateral damage as a Valar intervention. The way I see it, the Númenóreans by that point had surpassed even the Music of the Ainur (which is what Men are actually meant to do as per the Gift of Ilúvatar aka free will) and only Ilúvatar had the capability to stop them.
Or Manwë wanted to know how the Valar should act against Númenor. Should they just destroy the armies or the whole island?
Except that the whole destruction of Númenor and the changing of the world was described to be the work of Ilúvatar and not the Valar.
The Gift of Man is death. Through that gift they are made free of destiny. This does not mean they control reality. The Númenóreans could not have claimed what they sought because they sought immortality which is the exact opposite of the Gift given to them. The Undying Lands do not confer immortality. Frodo and Bilbo do eventually die even though they sailed West. Immortality is impossible to achieve for men by the decree of Eru Ilúvatar. The Valar didn't call upon Ilúvatar because they were afraid of the Númenóreans, they called on him so he could remove Valinor from the circles of the world to prevent anyone else as deeply stupid as Ar-Pharazôn from wasting their time committing highly elaborate suicide.
A good question, since Morgoth's claim that Húrin will see "through [his] eyes" can mean two things, either that he can see everything — for example, Húrin could see Morwen going to Thingol and soon leaving and Túrin trying to look for her a bit later while Finduilas was dragged away and killed as well — or that everything Húrin saw was distorted to give him more pain, focusing on the tragedy and loss and mistakes.
Some editions of The Children of Húrin include some explanation on this matter in the form of a short prologue by Christopher Tolkien. According to this, Húrin was semi-forced to look into Morgoth's eyes, and then either saw with his own eyes what happened or had visions of it. How much Húrin saw and how accurate that was is still a question though, but the explanation adds that Húrin indeed could have looked away himself and wouldn't have had to beg, he was just that desperate for infos, even from an unreliable source... and he was just that confident that he would be able to tell truth from lies.
Possibly the biggest mind screw in all the book but when Eru told Melkor that all things he thought he could make were merely an extension of Eru himself I realized that the whole fall of Melkor and his subsequent evil agenda were actually anticipated and factored into Eru's plans for the creation of the universe.
Eru's flame of creation, the only thing capable of giving free will and true life would be pointless if living things didn't have evil to choose apart from good. Melkor's deepest desire, of having that flame, which eventually drove him to madness actually stems from his existence being complementary to it.
When Melkor tried to destroy the realm of Ulmo with cold he inadvertently created all beautiful and marvelous shapes of ice and snow, and a new environment for Yavanna's creatures. When he tried to evaporate the sea, he created clouds that carried water inland. When he destroyed the Lamps he forced the Valar to replace them with even more beautiful creations (the Two Trees), and when he destroyed them in turn, the Valar created the Sun and the Moon... whatever evil Melkor does, it eventually has also good results that enhance the World. It is impossible having those good things without the evil that causes them and the eternal struggle between good and evil, so even though evil is and must be fought, its existence is necessary in the great scheme.