Hi there, I'd recommend also posting this into our motoring discussion forum too. If you don't find what you're looking for you can always ask Honest John he welcomes feedback on these kinds of things and maybe able to help.

Many thanks

Franchised dealers are notoriously inconsistent in their advice (and prices) for after-market towbars. I suggest you look for your nearest towing specialist, preferably a member of NTTA (easy to find by Googling). Regarding the rear parking sensors, the trailer will probably interfere if you have a cheap universal wiring kit fitted. The towbar itself shouldn't be detected, but you'll get an annoying continuous tone whenever you select reverse. Better, therefore, to pay a bit more for a vehicle-specific wiring kit, preferably BMW original equipment, and it will probably need to be coded into the ECU too. This way, your X3 will 'know' when it is towing and the sensors will be inactivated. There may be other safety-related features too, such as TSP, which will only work if you have an approved wiring kit and recode. Either your BM dealer or a specialist towing centre will be able to do this.

Like you, I'd be surprised if an uprated fan is needed.