It sounds like there is a short to earth within the lighter circuit. Best not put anymore fuses in until an auto electrician has traced back why it is blowing fuses in the first place.
Hi Tom.
I would definitely research that it has had Dealer servicing throughout it's history as it would be quite speciailist work no the R8. Also, that it has had any recalls and updates as well.
Also, warranty is uber important with a car like this.
Keep us updated on the purchase and would love to see some photos of it
Cheers, Trevor