Taken off evil-bay where I bought my kit:
This will enable your vehicle to have the full use of the cruise control unit already fitted to your 98 - 2004 Disco, Installation takes around 40 minutes to 1 hour.
Just to answer a few of your questions, Every single Disco 2 TD5 from 98 - 2004 rolled off the production line having had fitted the cruise control ECU, all the wiring looms, and absolutely everything required, apart from the switches. They were just dependant on wether the original customer build required this function, in which all that was to be done was to add a steering wheel with the switches and to fit the master switch. So yes to your questions, this kit is all that is required to completely add cruise control to your vehicle, but please feel free to ask any further questions, whether spec / fitting / fitting support.
Note: This is not compatable with the petrol V8