How did you figure out the capacity. I have a 535xi on order and want to change my oil more often than what BMW recommends. Are there any special tools required to change the filter? Is it hard to monitor the oil level and know when you have enough? I want to change the other fluids more often too. Any experience you can share would help. I am also concerned about the oil heat, especially with no oil temperature gauge. What is your experience? Doesn't sound like the oil cooler is any larger than the 335.
Figured out the oil capacity by putting in 6.5 liters (like the 335i takes) and after driving the car for a bit, the oil level was perfect. So 6.5 liters is what you should put in there... no more than that!
The oil cooler is definately bigger than the 335i, I would estimate about 3 to 4 times bigger, but this does not affect the capacity as they can keep enough oil in the sump even with this oil cooler.
To do the oil change, the only special too you may want to get is the BMW oil filter tool. I bought mine from Turner Motorsports... it is basically a cap that fits over the oil filter cap and it has a 27mm nut on the top. You don't have to get this as you can use a strap wrench, but the filter tool is much more elegant and makes life much easier.
As for doing other fluids, I have no experience to offer you on the 535xi as the car only has 8500 km on it so it hasn't been necessary to do any other jobs on the car.
Hope this helps.