Please be aware that if you have a CS1000M that uses the NT4N39AAE5 CPPIV processor cards you may be affected by the "dark card" issue when you try to power up. Essentially, if you remove power to the card, it may or may not reboot. It is a known issue and there is a bulletin about it. If you do have those cards I would strongly suggest you have replacements on hand (more than two)
That being said. Do you have any other equipment like CallPilot, Sig servers, etc.
If so, gracefully shut those down first, then shut the columns down column 4,3,2,1. I would unplug the power cords also if it is an AC system. I would power on when I was confident the power was stable, in the reverse order.
It goes unsaid to make sure you have current backups of all equipment.