Don't know if it is an optical illusion, but the clearance between the rear wheel and the wheel arch seems alot.
Seen quite a few of these and they have never been that distance apart. May be worth checking it out.
Tuning, take your pick, I had Revo and AMD, the advantage with AMD is a rolling road test before and after the re-map. Difference in performance between the the two, none, as far as I am concerned.
After chipping there is no difference between the 210 and 225 models in terms of performance.
I would choose the Xenon option every time. Make sure it has all the goodies, like leather, preferably black, heated seats etc. Alacantra trim looks nice, but accordind to a mate of mine, that has one, a pain in the ar*e to keep clean and if you ignore it, will always look like sh*t.
Bose audio is a must, especially for selling on. Some on this site reckon there are better systems out there for the price. Can't comment as I don't make a habit of comparing them, but I am more than satisfied with it in mine.
18" RSTT alloys, as far as I am concerned are a must, they make a classy car look just that bit more special, again personal opinion.
As far as mpg is concerned, I don't care. I get about 350 miles on a tank full, most of that is around town. I usually put £45 ish in when I fill up. If it is a concern for you, do not have the re-map, because if you do then the mpg will only go one way and that is down.
When I have my last one re-mapped, driving from the garage down a short drive in first gear, it was immediately obvious that this was a very different car. The difference is mind blowing and you will never regret it.
If it is due a service in the next 5k or so try and get that thrown in with the deal. Also, I would try to get them to change all the coil packs and if possible the MAF sensor.
If you encounter a problem with the MAF it is as if someone has turned off the turbo. It is an intermitant fault that does not always show up on a diagnostic check. When I buy my next S3 I would get this replaced, even if it was not faulty. I would keep taking it back and complaining until they change it.
Great car you won't regret getting one. Good luck.