Fitting D3 towbars is mostly a DIY job, both the removeable one and the multi height one, as the main mounting points are pre-fitted at the factory doing away with the need for a professional fit.
The electrics are also easy, just route the cables and plug into the waiting sockets behind the nearside rear light cluster.
What you can't do yourself is activate the system without a visit to a main dealer, or somebody with a faultmate or similar D3 compatible system to tick the correct box in the ECU.
Some people do run without this being done, but if it is done the car changes some suspension settings etc when it detects a trailer board is plugged in.
Another member on Disco3 did mine in a pub carpark after a local get together.
Remember also that using an LED lightboard plays havoc with the D3 Canbus system unless load resistors are fitted in parallel with the indicator LEDs to simulate the resistance of a filament bulb. The system detects a trailer board by sending a small pulse through the indicator circuit.
Just been over to Disco3 and seen you've already been told all this