I don't know the minimum thickness but if they are looking thin, I would suggest that it is time to change.
I had a partially seized caliper piston and my pads wore down to reveal the brass pins which hold the pad material to the backing plates. Luckily, they were caught in time and there was no damage done to the discs but the length of the pins I would say is approximately one third of the pad thickness so be aware!
I can't help with a Brembo part number I'm afraid and they tend to keep this quiet due to their deal with Maserati so good luck & let me know if you find it!