Which type of fat to make fudge? If you're making fudge, does it matter whether you use butterfat or vegatable fat? Or is it important to get actual, real butter?

For that matter, I've seen recipies for fudge which demand single cream, double cream or even clotted cream. What effect is this likely to have on the final product? (Taking into account that presumably whoever wrote the recipe already took into account the different fat content of these products.)
Like you, I've found a wide variety of fats in fudge recipes.  To name a few;

The chocolate fudge recipe in The Joy of Cooking cookbook calls for both half-and-half and heavy cream. (From my home copy of that cookbook)

On this Macinac Island website, there's a recipe that uses a combination of whole milk and Crisco (vegetable shortening).  http://www.mackinac-island-insider-tips.com/aunt-merrys-fudge-recipe.html

... and I found a recipe for Devonshire Clotted Cream Fudge that uses other ingredients I'm not familiar with such as golden syrup and castor sugar: http://www.food.com/recipe/devonshire-clotted-cream-fudge-238801

I think you may be obligated to experiment by making different kinds of fudge and discover your favorite homemade fudge.  Sounds like a sweet adventure!