"...how many cups of butters, oils, vitamin E, and fragrance I'd need if I wanted to make say a gallon or so of a body Butter..."
Wowser. That's a lot of body butter to make using an untested recipe. LisaAnne might have the bestest recipe in the world, but the recipe is only part of a successful product -- the maker and her methods are just as important.
I make 100 or 200 grams of an untested recipe to begin with, give this small batch a good trial, and usually make several tweaks before scaling up. I would need to KNOW I really like a particular recipe, know I can make it well, and know I can sell/use/give away the product in a reasonable time before I would leap into making a large batch.
For example, I was on Trial 7 of an emulsified sugar scrub before I was happy with the performance and texture of the scrub. My Trial 1 batch was based on a reputable recipe from an experienced maker, but it really didn't meet my expectations. Good thing I only made a 100 g batch of the base paste (everything except the sugar)!
I agree with SnappyLlama that a good scale is an absolute must. Volume measurements might be fine for a quick-and-dirty experiment, but weighing is honestly a much better and more consistent way to make B&B products and soap.