Scryers focuses more on Kael’s Sunfury/Firewings than Illidan, Aldor focuses on demons in general, only the Sha’tar, I think, has ever directly dealt with the Illidan topic.
I’m pretty sure you can change sides too later, but it is a grind to do. You can also read up on the quests from the other side if you are worried about missing lore.
No matter which side you pick, for the player, Illidan is the big bad of Outland until you finish the Black Temple storyline where that switches over to Kael’thas.