Rose offers assorted coffee-flavoured variations of silk meringue and classic buttercream in TCB which can also be applied to the mousseline. For a cappuccino flavour, you could reduce the coffee flavouring, increase the vanilla and perhaps add a pinch of either cinnamon or cocoa.
For the cake, you may want to consider the Genoise Tres Cafe (RHC): it has coffee flavour baked into it and is then syrupped with a coffee/Kahlua syrup. To reduce the strength of the coffee flavour, you can use this syrup with a vanilla genoise. The whipped mocha ganache Julie mentioned is the suggested frosting for this cake.