I would suggest going big and not having a worry down the road. If you have a lot of high draw add-ons (or possible plans for them) going bigger will not hurt anything


Main Ground and starter cables: 1/0
Power to fusebox 8 is "okay" but 4 would be better.
Fusebox throughout car will really depend on the item you are powering. Electric fans want 10 gage, lights and gages can get by with 16 and so on.


Because I have no idea what your experience level is with this stuff I will ask if you have the tools and connectors to do this correctly. PLEASE, do not use twisted wire and wire-nuts to make up this harness.


Once you price out the wire and tools and connectors to this correctly you MAY find it cheaper to simply buy a plug and play harness from AAW. and put it in...
Mark