I think you are confused about how surprised works:

> The GM determines who might be surprised. If neither side tries to be stealthy, they automatically notice each other. Otherwise, the GM compares the Dexterity (Stealth) checks of anyone Hiding with the passive Wisdom (Perception) score of each creature on the opposing side. Any character or monster that doesn’t notice a threat is surprised at the start of the encounter.

> If you’re surprised, you can’t move or take an action on your first turn of the combat, and you can’t take a Reaction until that turn ends. A member of a group can be surprised even if the other members aren’t.

The GM decides who is surprised, not the initiative roll.


So here is how that event would play out.

 1. Wizard teleports into combat
 2. Everyone Rolls initiative
 3. Turns start in initiative order
 4. Everyone who is not surprised gets to act while people who are surprised skip their turn
 5. Assuming the PCs have not teleported again before the end of round 1, round 2 of combat would start
 6. Turns begin to take place in initiative order, no one is surprised anymore

**EDIT to address scenario 3:**

The wizard cannot ready an action outside of combat, so he could not ready the teleport spell until combat has begun.