I'm going to clear this up once and for all.
1. All you need are 2 bloody fuses. As close to the + terminal of the battery as possible for the first one (ideally, on the post or mere inches afterwards) and one inside the vehicle at your distribution block. Each device should have it's own fuse as well, but that doesn't count since all commercial devices come with fuses already (part of certification). Fusing the ground is completely pointless, a total waste of money. The ground can short to ground all it wants to.
2. AC and DC switches are different. Do NOT use an AC switch on DC current. The contacts in an AC switch are much smaller, and open much closer together than in a DC switch. Because a DC current is not being interrupted 60 times per second (as household AC is), arcing can form when the switch opens under high load. DC switches have a significantly larger amount of contact material to deal with this, as well as more widely opening contacts to prevent the arc from forming. AC switches don't have this, and at the very least will wear out much more quickly than DC switches in a DC application. At the most, contacts may weld or burn, and if the DC voltage is high enough (probably not an issue here) arcing is possible (anything over 30V is a risk...think arc welder) which can cause the device to continue running, fires, etc. So only use DC switches in a DC application.