Glad you ask.
Does the order of actions mean that a later action cannot affect the results of a previous action?
Pretty much. It says in which order the actions are evaluated by the host - trap being the first.
Trap > RID Kill > Save > Redirect > Kill > Block > Oracle> Steal action > Spy/Follow.
E.g: If someone submits an action but was the target of a trap, his action is discarded since the trap is executed first. Saves protect from a Kill but not a RID Kill. Traps protect the victim of a Kill /RID Kill, etc.
Each game has its own order / rules set by the host, so nothing should be assumed unless explicitly stated.
Does Sela have a choice to RID kill or normal kill if her conditions change?
Nope. If she loses her initial targets she goes into a "murderous rage" - that is why RID Kill is replaced by a "blind" kill.
Does the Founder target a person or a role, and can she use acquired day abilities?
Founder targets a person, not a role. Practically, everyone targets a person.
Who is Omet'iklan's target if the Founder is killed at night?
Yeah, I left it kinda ambiguous, sorry about that.
He is a bodyguard of the Founder. So if Founder is targeted by X with a Kill (or a successful RID Kill) and Omet'iklan is still alive (not trapped), then Omet'iklan will die instead of the Founder and kill X /take X with him.
So more accurate would be: "If the Founder is targeted for a successful kill / RID Kill then Omet'iklan will die and take the attacker with him. The Founder will remain alive."
And in the unlikely event that the Founder is targeted by a kill AND a RID Kill the same night, then Omet will kill the RID-attacker (since that action comes first) and die leaving the second attacker able to kill the Founder.