I'm baking a 6 inch layered cake with a very popular doctored cake mix recipe here on CC, Heartsfire Durable Cake for 3D and Wedding Cakes recipe here: http://cakecentral.com/a/durable-cake-for-3d-and-wedding-cakes

I was wondering if I replaced the oil with butter, the water with whole milk, and the egg whites with whole eggs would it change the durability of the cake? I'd assume it would enhance the taste/texture and give it more of a "from scratch" feel to it. I just don't want to ruin the recipe.

Also, if I wanted to bake 3 6 inch cake pans and cut each one into 2 thinner layers, how many batches of the recipe would I need?

Thanks 

I think what you are suggesting will work just fine but have you considered using my *original* WASC recipe?

It's a very durable cake.  Here's a link to the recipe:  http://cakecentral.com/t/584319/the-original-wasc-cake-recipe