I have been asked to quote for a cake similar to the one I have attached but I have no idea how you you get the owl as smooth and perfect?! I'm thinking lots of maybe 6 inch cakes stacked and carved but surely it would be really difficult to cover in fondant?!

Getting the owl smooth all comes down to getting your buttercream smooth underneath. Stack and fill your cakes as usual and then carve. You for sure want to use a dense cake like a pound cake that will hold up well to being carved. Once you get the shape that you like, cover the cake with buttercream and get that as smooth as possible. Then cover with fondant. Covering a carved cake can be tricky though so go slow but not too slow that the fondant cracks.

For the ears, I would probably make them out of rice cereal treats or fondant so I could get them as pointed as I wanted but that is probably optional.