I share your difficulty, OP, in sorting out fact from fiction. I have so many theories sometimes I forget which parts are confirmed and which are my own crazy ramblings.
I think all we know of 'the big stuff' for certain right now is that Flemmy was possessed by Mythal (possessed isn't the right word, but whatever) and Solas is Fen'harel. We know the elves ruined their own society, but we don't know the specifics of why or how. We know Andraste did exist, but we don't know how accurate the stories about her are. I think the jury's going to be permanently out on the subject of the Maker -- I believe the writers have said as much themselves, that they don't really want to confirm nor deny his existence. I think we will be given enough information to make lots of guesses, and maybe be given enough to pinpoint a real person/being/spirit whose actions are attributed to that of the Maker, but as to whether there was an all-powerful creator who actually created all of life and the world, that's something we'll never know.
I think we've been given enough now to say for sure stuff didn't go down how the Chant of Light says it did. I mean, shit, the whole series so far has been one big lesson in "don't believe what you read or what people tell you." One of the biggest themes in the series is about how history belongs to the victors, and that stories will be rewritten, interpreted, have bits hacked off them, have bits added, and then be reinterpreted all over again so they don't reflect any of the truth of what happened. I always find it amusing when people blindly assume the Chant is an accurate historical document: "well the Chant of Light says X so we know that happened." Ha!
Basically, all of Dragon Age storytelling can be summed up in the very last codex entry in the notes section, entitled: "What Is Green?" It's a light-hearted entry, but at its heart it's saying "we interpret the things that happen differently depending on our own viewpoints, and who are any of us to say what is true or what is not?"
Hunting for that truth sure is fun though.