Main two things are turbo and the FMIC. The standard Cupra suspension is cack anyway and will need ARB's/springs etc to make it handle decent, same as what you would do to a FR/Sport.
Filter/de-cat/exhaust system is standard fare what ever car and you would do to a FR or a Cupra.
Brakes are a easy upgrade on a FR. £200 gets you TT/S3 calipers/carriers/hoses and 312mm Mintex disc andpads.
Oh and a remap would be needed for both cars.