Well to be honest we cannot really quote you what you need for parts from a front end impact without actually laying eyes on it as there may very well be undercarriage items, and other things not seen.
As far as going to a GT bumper, minimum you just need the bumper, you can get an 3D carbon grille with center fogs which does not require a surround or a saleen grille same deal no surround needed as its part of the grille.
Without those two grilles you will need the surround and then its your grille of choice and if you go with fogs in the grill you will need a wiring harness.
As far as everything else do you know if you have any wiring damage etc?
Why would you need a radiator with a 5 MPH impact? was it compromised?