Most things can be retro-fitted, its all a question of how hard, im no expert in this like some on here (ive only had mine for 2 months) you just need to replace the indicator stalk for one that has the cruise buttons, and activate it in vag-com and possibly a cable to the ECU. Im not 100% on this as the dealer did it for me, but from what I read it is one of the simplest fits.
And yeah you can retro the satnav, RNS510 is the best unit also know as the MFD3 (its what comes in the roco and MK6) there are some things that you need to watch out for but there are alot of threads and also experts in retro-fitting the nav units, so search and you shall find
The most difficult things to retro are the highline computer (especially on newer 06-07 cars) MFSW (multi-function steering wheel) and the xenon lights, so you are better off making sure you have them as original fit, if you want them rather than cruise or sat nav.