What is a level zero pyramid?It’s a pyramid that has not yet been placed on the board - an empty space in the city.
If I have a white level 1 pyramid, but I have control of an opponent’s white level-4 pyramid, am I allowed to buy white level 4 power tiles?Yes
Is it possible to upgrade an opponent’s pyramid that I’ve conquered and so gain the VP if I upgrade it to a level 4?Yes.