The first 2" headers I had, literally scraped past my starter, it's soo damn tight down there.
The turbo that's now down there, the compressor housing sits right beside the started, with the journal housing/turbine almost straddling the bellhousing.
I never really added any wrap etc, I chose to let airflow keep them cool for the most part, as sometimes wrapping things can almost make matters worse, as when heat gets in, it almost cooks things. At least when air can circulate that wont happen.
At most just a little shield perhaps to prevent radiant heat when stopped, but it will also prevent heat build up too.
my turbo on that side
and when it had the 2" headers, they had to scrape that close past in order to clear my steering linkage. It was a miracle squeezing them in !
I've just some 35mm^2 welding cable from the battery in the rear to the starter up front, battery is just a big 6-700A type.
But even once trying a small dopey race battery, it started the car fine.