you don't have too in fact it works best without a fuse, but at the same time your giving up safety if the wire comes loose from the alt it will short out and damage your battery as well as possibly start a fire/explode. I like to double stack fuses on that lead if in a crash and shorted it will blow but it will take a sec.
yep max rating, if you look what that is on 3' of 0g you will see why i double them up! and if you check across the ohm/resistance load of them doubled you will see a nice difference!
ABSOLUTELY fuse it, and a 300 amp fuse is spot on.. 1/0 gauge wire varies brand to brand, but 300A is right., Some people will disagree, and say fuses aren't necessary, but they are WRONG. ESPECIALLY between your alt. and battery. It WILL NOT have any EFFECT on your systems perfomance.. BUT, IT WILL protect your system. Fuse it or lose it. Hope i helped you bro... Bring on the haters.