Great choice then, glad you're enjoying it. Mine has 120K+ miles on but still drives like new, proof it's been looked after and the two previous owners to me are forum members.
I had an issue mid 2014 which happened after I'd had the car around five months and done a few thousand miles. It's all detailed in the relevant D3 section (Fuel and Exhausts, thread title is Emissions Control Warning or something similar) I'd post a link but I'm on an iPad currently and struggle with it. It has the highs and lows of a couple of months but is useful for reference should you experience similar problems, and could save you heartache and cash
Send me a PM if you have any further questions regarding this but generally everyone on here have answers to most major problems on A8's and S8's. It's a friendly place so if a search doesn't get you the answers you're looking for don't hesitate to ask.
On another note, if you haven't got your exhaust flaps fastened open already, you need to
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Audi D3 S8 - 2007 - V10. B&O, Phantom Black, black and silver interior, and still completely standard with everything working as it should
Audi TT - 2015 - Ultra