You wont be using any of that, nor will you end up using the stock gauge stuff, but do NOT cut anything from the dash area until you have the harness out, unless you know for certain you dont need it, like the power window motors etc
Everything going to the back of the car in the passenger floorboard area can go, there is a very thick patch of cabling there to cut free. Things that are hooked up to fuses relays I would keep. Since I am not done with my setup I will stop there, I have seen only a little bit out there on wiring stuff. Basically you have to pull it, and figure out from there what you need. I am going to shave down my harness mostly due to weight/size, otherwise you could carry over the whole thing and only use what you want, but it would also be more confusing that way.