[Q]

"1.) The AI launches mines in the sector of his colonies: That's something I haver never seen before and just excellent!!

At which turn did you notice this? At turn 150 none of the 6 AI empires have put out any mines in my current game."

About turn 40.

PS: I switched all players to human control to check this. Two empires were using mines in the sectors of some of their colonies: the Xiati and to a lesser extent the Abbidon.