the tauras fan uses about 25 amps when it is running. it has a large amperage spike when you first turn it on of around 50 amps but quickly drops to 25amps. if you dont have any other aftermarket eletrical accesorys that pulls high amperage then the stock alt will work with that fan. if you have air conditioning, a big mulitamp stereo, eletric water pump, eletric fuel pump, etc, then you will want to upgrade to the 100 or 130 amp alt.
I wud recommend going w/ one wire altenator; eliminate the ext regulator and all associated wires. That's what I did.
I would go at least 130 amp, actually I installed a 150 amp when I went to a Taurus fan. The alternator doesn't produce full current at idle, which is when your fan will mostly turn on. And if it's night time with lights on, brake lights on, stereo, ignition, etc. It adds up pretty quickly.