If I was in your situation, I would wait until the cat's first offense. We have had feral cats hang around our coop, a few which have starved to death, and haven't had a problem with cats yet. Cats usually(I know there are exceptions people!) prefer smaller prey. If the cat is a pet it is most likely well-fed, so it will not hunt your chickens as food. I would think that a cat would need be hungry to take on something as large as a chicken, hence why most feline chicken-eaters are feral.
If the cat does bother the chickens, I would talk to his owners first, especially if you are on good terms with the neighbors. Most people are very understanding when it comes to their pets, and then there are those that aren't.
If the cat does something offensive, ask the owners to keep it contained, and if it occasionally gets out, be understanding(don't shoot or trap and remove it the first time it makes a 'great escape')
I don't think you will have a problem with it, but I could be wrong. Keep the chicks and smaller chickens secure, standards should be fine. The water hosing idea sounds like a good one, firecrackers(the loud ones that flash and pop) are a good "traumatic" deterent too.
-Kim