The marina probably isnt a Honda dealer and is having to pay to many middle men, either that or they are just trying to rip you off because suggested retail on the Battery Cable Harness assembly is $145 (can find it for even less online). The part number that i think it might be is
32410-ZZ5-000 (would need serial number to confirm) and for what you can find that part for online i would just buy it. It comes with all of the fittings and boots to properly secure it and you know its the right size/type wire and terminals.
If you make your own out of #4 wire you probably will have a really tough time fitting the grommet that also helps hold/protect the control cables and wiring harness.
The green connection is for the warning lights, most of the time it is a seperate harness. But you can buy a main engine wiring harness with those wires built in too.