You will probably need to try the dsg before you decide, many love it. Personally I think it's good but with some drawbacks. It can be slow to respond, has too many settings imo and would've been smoother as a proper full auto. I also think it takes some of the fun out of driving, my old PP manual was often more exciting so given the choice my preference would be a manual. In 40k miles I had no clutch issues. On a positive note for the dsg, it is a very relaxing drive and if you like cruise control it works better with that. On the other hand though the stop/start system is much better with a manual, on the dsg it doesn't always cut in when it should then if the car in front moves an inch the engine starts even if you don't intend to move.
PP isn't a must have, more a very nice to have but for the GTI on the calipers alone it is well worth it! I would go for it if I were you.
Leather? Just bear in mind that not all of it actually is leather.... Plus the tartan is rather cheery.
Costs wise, on a MK7 the waterpump/thermostat housing is a very common failure and if it hasn't been done I'd have some funds set aside as chances are they will go and probably fairly soon. Batteries are expensive too. The turbos on early cars could be problematic but any dodgy ones would likely have been sorted by now.
If you can push it to a 16 plate you should get the later MIB2 with a slightly bigger screen. Also keyless was standard along with heated seats. On early 15 plates nav was an option too to bear in mind.
