If the total distance from the (Batt +) through the entire circuit (to the windlass motor) and back to (Batt-) is less than 50ft you can use 6ga wire for the windlass, so long as you don't run anything else on the circuit.
I would run the windlass circuit separate from the "house" system just to keep connections to a minimum and to prevent a windlass malfunction from affecting the rest of the boat. ( for example, a bad ground connection may cause the windlass circuit to find ground through the "path of least resistance". (hope and pray the "proverbial path" is not through an expensive piece of equipment)
Running the "house" circuit separately, you can probably use 8ga depending on the rest of the equipment you have installed.
EDIT: This is just my opinion, without having ever seen your boat. I am certain Les has already installed more windlasses than I ever will. Honestly, 4 a year is a good "windlass sales" year for me.
I would run the windlass circuit separate from the "house" system just to keep connections to a minimum and to prevent a windlass malfunction from affecting the rest of the boat. ( for example, a bad ground connection may cause the windlass circuit to find ground through the "path of least resistance". (hope and pray the "proverbial path" is not through an expensive piece of equipment)
Running the "house" circuit separately, you can probably use 8ga depending on the rest of the equipment you have installed.
EDIT: This is just my opinion, without having ever seen your boat. I am certain Les has already installed more windlasses than I ever will. Honestly, 4 a year is a good "windlass sales" year for me.