We can't really give expert advice on this subject beyond that you've already had from the fitters, who will know the full story - we certainly can't give you a figure for what it costs either. Regarding recoding, this is to do things such as disabling the rear parking sensors and any blind spot warning, disabling the rear foglights and to have the car give you an audible warning when a caravan or trailer bulb has failed. Most fitters should be able to do this in-house and quote you on the cost as part of the whole fitment.

Regarding fitting a detachable towbar, this is necessary to allow your rear parking sensors to work. Without detaching the towbar the parking sensors will need to remain disconnected.