May as well just fit the mfa function as well, it will be easier.
Loom wise you will need to fit engine bay loom from gti, and front to rear loom from the gti as well as the small loom piece down to the undercar fuel pump.
If the ryder does not have central locking and the gti does then swop the bootlid loom as well, you will need to swop the dash loom as well possibly, you definately will if you want to keep the gti heated washer jets
May be a few extra relays etc to fit as well but you may as well just swop the fuseboxes over