BMW will quote you a fortune but you can get it fitted for about 1/4 of that - or possibly less. Their charges are completely unjustified and just taken off a menu of fitting prices. Having one added at build is £2k cheaper!
The OEM Towbar is made by Westphalia and is readily available. Have a look on the PF Jones website for the non-BMW badged Westphalia detachable bar. The bar with the correct 13-pin electrics is about £475.
The fan upgrade is to the main electric cooling fan which goes from 600W up to a bigger 850W unit. All factory ordered towbar equipped cars get it. Whether it is really needed is debateable and depends upon what you are towing. If the car is under warranty then you ought to fit the fan. It is to ensure adequate transmission cooling when towing.
What you
will need is a different rear skirt on you X6 as there is a panel you need to have added into the existing one. That will add to your costs.
Parts 10 & 11 on
this diagram. They replace part 9.
If you are going above 2.7T then you need a much bigger upgrade which adds grilles, radiator, fans and valve gear. It's probably cheaper to find a ready equipped X6 than have that fitted by BMW!