All rules are known. does that mean I can look at future missions or encounters as either heroes of OL?

Absolutely. Page one of the Shadow Rune/Heirs of Bloid says everything is always public info. For instance, while you're picking heroes/classes/OL decks, you are free to study the finale and choose a build to win that.

You can, and as the OL you absolutely should. Long term planning is key to winning a two-part encounter.