couple of questions for you

[Hydraa]

As to number 3 I would guess that the AI does not know what a stellar construction is. All it sees is that there is a system with no star. So it tries to create a star. It gets the error message that there is a stellar construction there but then promptly does not do anything about it.

A constructed world for just about all situations replaces the star with the constructed world.

Also I think the AI can only handle 1 of each type of stellar manip components. I once created two planet construct ships on opposite sides of the galaxy to create planets out of asteroids. Both ships decided to go to the same asteroid. It appears that the AI does not have the luxury of knowing like the colony AI that a ship is already on the way to do the stellar manip item.