@Shoduchi
Only MAJOR hesitation on 4WD is the cost.
Can imagine I won't see any change from £10k to finish her properly once I add in (potentially) a bigger BBK, Coils, side engine mounts, rear bushes, another map, a bigger cooler, RFD, 3 1/2" decat downpipe and that's on top of a Hyprid turbo, WMI , all other supporting mods and whatever the 4WD convertion would cost......ohh and a respray.
Or........
Put that £10k into another car.
RFD is a relatively cheap mod. You just need a bigger BBK if you're going to track the car. I don't think coils are mandatory. Good springs and good dampers are enough. You don't need WMI with a TTE420 to achieve 420 BHP. I think your 3'' BCS downpipe with sports cat can handle the TTE420.
I'd do the 4WD, then the TTE420, the TTRS LPFP, the 155 bar FPRV, RFD, the side engine mounts, the rear bushes and another map. If the IC was compromising the performance then you could sell your THS and upgrade to a Peron.