A couple of points not mentioned yet -
The steering wheel mounting nut (10mm hex socket head) is installed with industrial thread locker. It may take a butane torch to heat it enough to loosen. If so, beware of fire in the cabin.
Be sure to mark the location of the steering wheel on the spline. If you look closely you'll see two splines missing. One at noon and one a 6 o'clock. Place a felt tip marker in that space and use it to transfer a mark to the other piece. It's easy for the wheel to look straight when reassembling only to find out that it is off one spline as you drive down the blvd. Very annoying.
You can support one of the arms of the steering wheel from below by standing an appropriate length of 2x4 or similar between steering wheel and floor.
Any T30 bit 2 1/2" or longer will work. As mentioned, DO NOT turn on key while air bag is disconnected. Error code will require dealer as I am told. Didn't try to find out. So make sure you have moved the steering wheel (if adjustable) to the appropriate position before disconnecting battery.
The bracket which holds the combination switch (CC and Turn Signal) must be a specific distance from the end of the steering shaft. I have attached a WIS diagram showing the distance and where to measure. If this distance is off, you may have squeaking or grinding sounds as you turn the steering wheel. The critical distance is 'b' in diagram -- from front surface of combination switch mounting bracket to that ridge near the spline. It is 30mm.
Torque for airbag fasteners is 8Nm and for steering wheel mounting bolt is 80Nm. No spec on other fasteners. You may want to put a dab of thread locker on the pinch bolt (phillips) of the combination switch bracket. This often loosens over time so a good preventive maintenance.
This procedure should apply to all W210's. Maybe with slight modifications.