Specing your 911 is very personal, such opting for PDK or manual may well be an influencing factor. Will the car be mainly be used for commuting to and from work or mainly used for weekends or both. Some people are happy with the basic stereo and the basis seats. You need to sit in one and go for a test drive and then make your decisions based on the information gained. I do not think you can spec a 911 without first driving at least one.
Such as I have ordered a manual and not a PDK, however I have Spec'ed 4 wheel steering and sports suspension. Its all to do with person preference.
You may well find it more cost effective to buy a ex demonstrator or one with a previous owner if cost is a influencing major factor. There are a few 911.2 now available in the 2nd hand market. There is a red 911.2 for £97,990 at
http://www.pistonheads.com/classifi...1-carrera-991/porsche-911-carrera-pdk/6184388 I would expect you could get some discount on this as well.
I have read that some journalists prefer the base more so than the S. You could go with the basic exhaust and get a aftermarket one fitted later.
The added optional extras on a 911 are just icing on the cake.