IIRC the one-wire alternator was developed primarily for the hot rod crowd because it looks better and doesn't require as much wiring. Back in the day, they didn't start charging right away, but had to get over a certain rpm to start charging. So they're okay for a garage queen, but I wouldn't have one for a daily driver. Here's what the MAD website says:
http://www.madelectrical.com/electricaltech/onewire-threewire.shtmlAbout size - well, it has to fit. Size? Think of all the things you are going to be using on your car, find the max amps and add. As you won't probably be using everything at once, the total of all the max loads should be sufficient.
Again, back in the day, upgrading from a 37 amp alternator to a 65 amp one was the thing to do. Now, I'm guessing you will probably be looking at a 120 amp alternator. Keep in mind that modern electronics are becoming much more efficient, like the newest amplifiers, also LEDs for lighting. To calculate total lighting load, add all the wattages from all the bulbs and divide by 12. Electric fans are an area I have not explored.
Good Luck!
R.
