Regarding wiring, I didn’t use the 3rd (square one) of the 3 connectors on the outside of the battery that supplied the car’s hvac stuff. I just cut that section including the socket off the aluminium metal work. So any wiring that connected to that on the inside of the battery was left out in my build.
It’s possible in the future I may get back to wanting heating, but I’ll cross that bridge when I get to it.