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.
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.
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 Numenoreans were their empowered descendants and they were at the height of their power so there's actually a good chance that the Numenorean 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 Numenor for fears of collateral damage...until you realize that Manwe invoking Illuvatar caused just as much collateral damage as a Valar intervention. The way I see it, the Numenoreans 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 Illuvatar aka free will) and only Illuvatar had the capability to stop them.
Or Manwe wanted to know how the Valar should act against Numenor. Should they just destroy the armies or the whole island?
Except that the whole destruction of Numenor and the changing of the world was described to be the work of Illuvatar 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 Numenoreans 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 Iluvatar. The Valar didn't call upon Iluvatar because they were afraid of the Numenoreans, they called on him so he could remove Valinor from the circles of the world to prevent anyone else as deeply stupid as Ar-Pharazon 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.