Can a single Action cause a trigger to happen multiple times? Eg, if Heart of the Wildfire's Presence moves to multiple lands in one action, or if The Kingdom of Scotland Level 5+ cascades Blight from one Coastal land to another?

Can a single Action cause a trigger to happen multiple times? Eg, if Heart of the Wildfire's Presence moves to multiple lands in one action, or if The Kingdom of Scotland Level 5+ cascades Blight from one Coastal land to another?

No. A single action invokes a triggered action exactly once or not at all. If the effects of a trigger are variable, it will say so in the trigger's effects (e.g., "Vengeance of the Dead" deals "1 Damage per (piece) destroyed" rather than a flat amount).
If Finder of Paths Unseen moves Heart of the Wildfire's Presence to many different lands, "in the land it goes to" is ambiguous and Wildfire's player chooses which land its "Blazing Presence" special rule applies to. If a since Ravage action adds Blight to two Coastal lands (by cascading), "Runoff and Bilgewater" (The Kingdom of Scotland Level 5) adds a single blight is to that board's Ocean; if the two lands were on different boards, "that board's Ocean" is ambiguous and the players choose which it applies to.
A single action can cause many separate triggers to fire, including separate triggers that come from the same Power Card — e.g., if "Vengeance of the Dead" is Repeated on a land, each use of the power sets up a separate trigger.