Mostly the story is just that: a story. Should I choose to use it as the background for an RPG campaign, it'd take place over the whole timeline, ending with the final climatic battle with Morgoth. My only player is my brother, who would have the choice of being a Noldor, Teleri, Sindar or Nandor.
Now, I have still never got that far into Silmarillion (maybe 1/5 of it). But do yo know how you want it to end, or things in between you want to happen? Put those in, and then work from there. You will most likely rewrite things to connect it. But then, that might be things you would have needed to rewrite anyway to get everything coherent, even if only adding things in the order that they would happen.
Hm...that'd be a no. I really didn't think about it. I mean, yeah, a big final, climactic fight. But I don't know who'd initiate it; Salmar or Morgoth. I'm really stuck after what I've written.