It's certainly true that a lot of people use an island to protect ducks from foxes although I know that foxes can also swim. We have a large pond in our new house which has 2 small islands on it and we have wild mallards on it which have raised young this spring happily so presumably it does help. I suspect that in a rural environment our foxes are pretty nocturnal and not so keen at swimming in the dark!
The problem is that it needs to be a pretty big pond to offer this sort of protection. I can't really let all mine onto the pond as there is too many of them and they would destroy the wildlife that I am trying to encourage there! Ducks are also pretty stupid and I suspect that half the time they would sleep on the "mainland" and then be vulnerable
Ducks certainly love a big pond but are also happy with a paddling pool to wash in. The advantage of a paddling pool or smaller rigid pool is that you can empty it and refill it with fresh as they need.
Mine have a small pond in next doors field which they have cleared before it dried out and 2 paddling pool things that I fill every day for them.
As to quiet ducks, not many are!
I started with Campbells as they were recommended as quiet and they were incredibly noisy! Runners also seem a bit noisy. Calls are meant to be very noisy but never had them as they don't lay much and think they look a bit odd! Some of my bigger ducks are pretty quiet and I am a big fan of Saxony's which are beautiful, lay well and are very tasty! Ultimately have a look round and find something you like the sound of in terms of what you want. Then have a look at them.