I can't see why you need an oil cooler on a road car, especially in UK. We don't really need them, even with hot summer here in Greece. Difficult to reach high enough temp to justify the oil cooler. I can't imagine you drive everywhere flat-out...
Try to adjust camber from the lower mount and not on the top. Adjust first the top mounts near the most negative value and only fine tune camber from there. This way you increase scrub radius that will make steering more positive.
This is a kit for 14" wheels, 6 pot small size caliper. WMD has a 14" kit but this is rare, not like jam/blitz/... P&P ecu rare, really rare. It's the only one seen for sale...
If you don't want to really mess with the car, then go with the PFC. Plug and play, so in any case you just go back to stock. You can make very good tune on PFC. Its just a good use like a runnable stock ecu. Nothing more nothing less.
Ideally stock injectors run on logical duty cycle at around 200 HP. Higher power would need larger injectors. Usually 550cc from rx7 turbo. 3sgte injectors are sidefeed so not going to fit.