There's a few wire size tables and calculators on-line.
Engine compartment runs at higher temperature, so voltage drops increase.
SAE gages have lower carrying capacity than AWG (Marine wire uses AWG sizing) WireSizer User Guide Wire Size Calculator
By disconnecting the hot Wire from the alternator to ammeter will I lose power to the fuse box or will it still get power through the ammeter from the other side?
it reads like it will be getting power from the 'battery' side of the ammeter.
Another way to kill the engine with a 1 wire alt, kill power to the msd or the msd on/off wire. Then you don't need to use such a heavy duty continous relay.
Fusible links IMO should be between the battery and anything that is running without a fuse. I've been making an exception for an MSD 6 power, but am now in the process of changing that. I assume your electric pump is power is fused.
