Ooookay. I got the car running. The fuel feed hose from the tank ruptured dramatically, so I had to wait until Tuesday when Pirtek opened up again to get replacement hose as no-one else sells high pressure 1/2" fuel hose. That's all sorted now, although I need to jack the car up and tidy it up still.
Today I fully deleted the old alarm system, all the wiring, splices in the harness, etc, all have been reverted to stock. I removed the bonnet cable using this guide and flushed crud out of the sleeve and re-installed the retainer ring in the firewall. Bonnet cable now buttery smooth!
Next I deleted the bodgy windscreen washer setup, removed the aftermarket washer pump and wiring and soldered in a stock connector and fixed the original pump (there was nothing wrong with it, it just had some dirt in it, I ran it in reverse with some water to clean it out.
Next up I am ordering these parts from VP Auto:
New tail lights are a must, the old ones are hot garbage, lenses are faded and so on. Brrrr sticker is also a must.
Other than that, we have a battery hold-down clamp and a complete new lock and key set. Apparently people don't know you can just buy a new lock set and so they drive around with four different keys two of which don't work on any lock and a broken passenger door lock and a driver's door lock that doesn't have a matching key. Cool!