I need help please! Someone requested a not so sweet buttercream (like a whipped buttercream). It would be nice if one existed that crusted and was good for decorating but that's not a necessity. I have never tried IMBC. Is that the way to go? And if so, what recipe? Thanks!

Yes, definitely try a meringue buttercream.
This is a good one: http://cakecentral.com/recipes/the-well-dressed-cake-swiss-meringue-buttercream-with-variations/

http://cakecentral.com/recipes/extra-special-buttercream-icing-recipe/