According to multiple writers, the map is not to scale. Shurima, for example, is supposed to be larger than Valoran.
We also know that the map represents ~1/6th of the actual globe, of which the map shows the upper western hemisphere.
There is a lot of Runeterra that remains yet to be seen. More recently, with Ruination (the novel) we got a glimpse of more of the landmasses to the East. (More specifically, part of the continent that holds Camavor and Kathkan.)
Hey, always great to see someone interested in Lore.
League Universe (https://universe.leagueoflegends.com/) is the official site, has all the stories, bios, comics and cinematics.
There’s an option to explore region by region, thus reading all the champs and stories associated with each. Thus giving u a cohesive storyline. There’s also an option to read champion by champion. The order doesn’t matter really. For stories that are directly and immediately tied plotwise, they generally have a “part 1, part 2, part 3” system.
An “Explore” option is also there for you to see the stories by release date.
As of yet, regarding sources of Lore outside of Universe, there is the garen novella: Garen: First Shield. The Realms of Runeterra companion guide (has 6 unique/exclusive short stories), Ruination (the novel released this year), and The Ruined King game. As well as the animated series ofc, Arcane (on netflix).
You can also hop on the Lore of Runeterra Discord (https://discord.gg/EbFjyvy) server and subreddit (r/loreofruneterra/); bunch of people who are invested in lore who are always happy to welcome new people and help them along the way. There are intense discussions as well, with theories abound. It is also somewhere you can choose to be notified when new lore drops. (We have a bot monitoring it.)
We also get the writers and members of the Lore division of riot, so we sometimes get the inside scoop haha. Regularly communicate with Lead Narrative as well. Pretty big community, and is honestly the best discord server I’ve had the pleasure of joining. Ask for Aether (or anyone u see typing really) if you need help navigating.
The Lore of Runeterra subreddit has also done a couple guides to help with streamlining information and stories:
https://www.reddit.com/r/loreofruneterra/wiki/guide
https://www.reddit.com/r/loreofruneterra/comments/i8g6js/a\_smaller\_introduction\_to\_league\_lore/