Each of those items will have either a power rating or amp draw at nominal voltage.
Most things will draw more at higher voltage so if the nominal is 12 then figure it will be higher at 14.2 or 14.5 V.
Add 'em up and you have a good idea of the additional load you'll want the alternator to supply. All of those items will draw at idle speed so tht's key thing to find out about the alternator. How much power can it supply at idle speed? If it can't do it at idle, then the battery is going to take over. Some higher rated alternators have worse idle performance than their lower rated counterparts.
There's an output curve for a "78 amp" Chrysler revised squareback you can use for a baseline comparison to whatever you're looking at. You'll need to know the pulley ratio to convert to idle speed.
Shown in these two posts: bouncing volt and ammeter Adjustable voltage regulator...how to adjust?
