AI am doing a two layer cake that will be 12x18 filled with Carmel sauce , I am wanting to know should I use butter cream frosting or will cream cheese frosting work just as we'll. my daughter does not like butter cream as much.

Earlene Moore has a GREAT cr ch b'cream recipe.  Do a google search for her site - the recipe is on there.

http://www.earlenescakes.com/icings.htm

Also will the cream cheese frosting allow me to add some decorations on the cake. I adding a 1 Direction logo made out of meringue on to the cake, with some chocolate signatures.

Also will the cream cheese frosting allow me to add some decorations on the cake. I adding a 1 Direction logo made out of meringue on to the cake, with some chocolate signatures.

Adding meringue decorations  - do that at the very last second before displaying the cake :(  Any moisture will cause them to soften/ loose their shape.

Unless you are referring to what Wilton calls/(or did) meringue icing which is really royal icing.