So if I am running an isolated/floating ground for the EFI portion - I'd imagine that the wire size vs load requirement would be downsized quite a bit when compared to the wire size / load requirement for the starter, lights, pumps and fans.

I'm thinking I could get by with a #6 wire for the isolated/floating ground portion, then go with an 00 run up to the starter/chassis itself. All sensors and the standalone computer get their own dedicated grounds running to the bus bar isolated/floating ground.

Does that sound right?

The only place I see a conflict is with the crank and cam sensors. Won't they see both grounds just thru contact? And can that negate the "floating" part anyway?