Welcome to the forum Ali, you'll find the members on here are a friendly and helpful bunch :)
You've gone for one of the better specs :) but have to agree heated seats and xenons are rare.
Key thing is check service history, ideally this should be full. If the car has had any oil consumption issues there should be proof in the service history of any work carried out.
With regard to the s tronic gearbox, make sure the gear changes are smooth both in auto and manual modes and free of an judders as any issues can be expensive to fix.
Also make sure all electronic items work as some of these can be expensive to fix. This also goes for the air con as compressors etc can be very expensive.
My order advice would be for you to ask the seller if you can get an independent inspection carried out. Companies such as the AA and RAC offer this service. If the seller is reluctant or refuses then you have to wonder what they or the car has to hide.
I've found this YouTube video which maybe useful :)
Hope I've helped :)
Cheers
Steve