As with everything this is just MHO. Feel free to take with a grain of salt!
With regards to wiring, speak to some of the more "clued in" people around the forums and club. For example, if you were doing a 20V I know of a guy who is finalising a prefabbed loom ready for a AE86 install. He was also toying with doing one for a 4AGZE into AE86. Of course this convenience has a price - which I don't know sorry.
I've learnt heaps by working on my car over the years. And I now know where my limits are when it comes to certain types of work (like welding ).
When it comes to breaking stuff the former Toymods president was legendary. But it comes down to how you drive it - if burnouts and flat shifting are you then get ready to stock pile diffs and GB's. Thats not me and I've only broken one diff and gearbox in 5 years with the Z (inc a few track days and quite a bit of touring).
You also need to think about insurance.
Like Widowmakers signature says "if your not an AE86 man ..." don't bother with it. Leave the car to someone who is and get something else.