Thanks for all your comments.
My imac is actually reaching capacity, so think will get the mini to store music on as well as movies. What is the difference between the apple tv and a time capsule?
I think I am going to get an audiengine 5 speaker system which has a dock for the airport, so I only need to position the speakers, plug in the mains, airport and go. For the roof terrace I am going to buy amp with a dock for the airport and put this near where the speaker cables will run.
Or I could if I bought a proper amp (preferably with a airport dock) that could run 4 speakers put in in the living room, and run cable all the way to the roof terrace......can anyone suggest one?