a few of the turbo setups i've seen on the web over in the USA run the same true dual as me the invidia G200/G300
not sure how much of a difference the exhausts make once you go down that route, but its good quality. originally they were about $1000 dollars or more, but they've come down, especially on the older G200, think they are about $800. another option would be to look at a custom build; hayward and scott are very good and build quality systems for all kinds of car. to give you an idea on price they quoted me around £550 for a cat back system which you could specify your own tips, pipe diameter, back box style etc.
as for brakes if you already have brembos i'd say look at the full DBA or Dixcel setup just uprate discs and pads. or go BBK and if budget is an issue possibly the K-sport system, bennett seems to like it.
as for the rest i'm into unknown territory, poeple like zmanalex will have a better idea,