A circuit breaker is Never a bad idea IMO, just make sure it is sized to handle the amperage of the alt..
Most boats wired with an ammeter used a heavy orange and a heavy red, ooh never did that before that was cool, if you only have one red then it is ok to use that but run a continuous wire from the battery to the meter, then a wire from the ammeter to the "batt." terminal of the ign. switch with a separate fuse for the Ign. sw., the ammeter will be taking on all of the amperage generated by the alt...It should work exellent...
Just make sure the ign. switch power comes off the "Batt." side of the ammeter. (Red wire.....)
Let us know how it turns out!