Nothing has helped me more than browsing the very Wiki you're on right now. As soon as I came a cross a name or a date or an event, I looked it up here. Incredibly helpful to get a proper grasp on the Silmarillion and all that takes place within it.

I don't mean that, I mean did Tolkien try to expand the plot, dynamic or character development in any books regarding to characters in the Silmarillion? Just like how GRRM write Aegon V in Fire and Blood, while also add another story The Adventures of Dunk and Egg which is about the life of young Aegon V and the knight same Duncan.

I know he did in books like Children of Hurin and Fall of Gondolin, but there's so many characters deserves more elaboration, like a story focusing on the House of Finwe, Thingol's reign and his love with Melian etc.

You can get a bit more in the books Beren and Luthien, Children of Hurin, and Fall of Gondolin. Overall though, Tolkien wrote these stories more as legends than as novels, so you aren’t going to find the same kind of character depth in someone like Turin that you will in Frodo or Aragorn.

Try reading The Unfinished Tales. It has a lot of useful definitions about topics The Silmarillion and the other books have just mentioned, not even explained. There is an important amount of information there that may help you get a more complete idea of Middle-Earth.