There is Buttercream and American Buttercream. Buttercream is made with shortening and American Buttercream is made with butter. I think that's how it goes. You can also make Buttercream half shortening half butter. I personally make a...
Not sure if this will help you. Its buttercream on buttercream, not sure if black buttercream will bleed or not and how well buttercream will hold up in a long car ride.
Op I sent you to www.cupcakeproject.com the ultimate vanilla cupcake recipe on that site gives pretty good detailed instructions on making that particular cupcake. Baking powder and soda have expiration dates on the packaging.