Calculating alternator requirements

FIRST question is "what about wiring?" If you have a factory harness, running more than about a 45A is foolish:

On this website:

MadElectrical.com - Electrical Tech

read this article:

Catalog

On a side note, before you "jump into" electric fans consider this:

They are not a cure all, and there's been "several" members on here who have had nothing but troubles. Not enough fan, restricted airflow, etc. Bear in mind YOU are "re-engineering" the entire cooling setup. So base your fans on what others have done "that works." GOOD fans draw LOTS of current. There is no way around it. You might just consider 'not' using them at all!!

Once you know what you are going to do in that regard, really, it's a simple matter of adding up accessories and deciding "what all" you will have online at the same time, plus some headroom to charge the battery afer starting.