Re: to fuse or not to fuse
The basic concept is that the fuse is no larger than the current carrying capacity of the circuit it protects.
Start with the motor. What is it rated for? If this is a new motor you probably have a manual that will tell you what to fuse the motor for. If not try to do some research.
If you have that you can determine the size of the wire you need to run to the motor from the battery. There are 2 factors to determine minimum wire size. It needs to be big enough to keep from overheating and burning up, and you want to keep the voltage drop below certian levels. (Voltage drop is the voltage you lose in the wires).
A rule of thumb for current capacity is that 12 ga. will carry 20 amps and 14 ga will carry 15 amps. You then double the current for every 4 gauge sizes you go lower and halve it for every 4 gauges you go higher. So if 12 ga will carry 20 amps, 8 ga will carry 40 amps, 4 ga wil carry 80 amps, etc.
Voltage drop becomes a factor with long cable runs. With high current and long runs you can start with 12 volts at the battery but only have 9-10 volts at the motor. This causes the motor to bog down, draw more current, heat up, etc. Think of what happens to your lights when the house air conditioner starts up.
It sounds like you are close to the battery so this is probably not a factor.
Not sure of your setup but I would look to having one heavy cable to the motor with a fuse close to the battery - about 6-8 inches.
Then put another wire with another fuse close to the battery to power the other gear you have.
Hope that helps.