In terms of ball size they use the one we do here, a 50mm diameter ball. The issue comes with clearance around the ball for van's with Al-Ko stabilisers.
If the Audi has a swan neck tow ball you have no further concerns, if it is a two bolt fixed one, then if the Hobby has an Al-Ko stabilising hitch a special ball is needed that has both a longer offset and long neck. These Al-KO compatible two bolt ball are readily available and these can be used on non Al-Ko stabiliser hitches, as well.
I fully expect an Audi factory fit will be the swan neck type.
The electrics will be the now normal 13 pin one piece type, but things like the fridge are unlikely to be wired up for powering whilst towing; in practice no great issue.