Stock alternator up to the task? If not, how many Amps will I need?

Power from Batt +, the ammeter will absolutely see fan draw as the alternator is going to be throwing charge both in and out of the bulkhead and through the ammeter when engine is running. Engine off, it won't see a sniff.

Fans are the toughest to pick a point as they can run in both engine on and off situations. Pick your poison. Do a wire around and the ammeter/bulkhead doesn't really matter much in either engine situation.

A good Denso 65-85 amp alternator off a toyota PU will usually provide enough output at idle for our cars without a bunch of additional accessories. No need for any 150 amp units. In proper operating function, the alternator will only put out as much as is required by the system. A bunch of overhead power is a waste IMO.