I'll see what I can answer with what I know about events, not scripting.
In order to set something to be locked simply have it require a switch to be unlocked. So for example
Page 1:
Event picture: (Grayed out version of a city)
And nothing else as it can't be interacted with.
Page 2:
Event Picture: City, normal color
Requirement: Switch 100 (note NOT self switch as those only effect that particular event. If you want multiple places to be unlocked use regular switches)
Transport to Map 3...or whatever map you want and select where the player starts.
Pretty simple for the most part.