Gruff is easy, insightful is harder but I will try.
I had ponds up in Upstate NY, serious cold. And I've had ponds in mild climates, San Jose CA. That's were my experience is coming from to help you judge.
If you get ice on the pond sometimes that melts by afternoon you'll have no problems. I remember people in San Jose freaking out when there was 1/8" of ice on the pond in the morning..."Should I buy a heater?",
A cold spell for say 5 days where the pond is iced over you'll have no problems.
14000 GPH might freeze up in Upstate NY some years. But in that case the way bigger concern imo is cooling the water to the point of fish dying, even Rainbows. But I don't see how you could get anywhere close to being in that boat in Settle assuming reasonable elevation. I've read of people in Sweden having these kinds of problems.
Small point...
This small point doesn't effect you, but I find it very interesting...Your pump only appears to have "closed spaces". The input pipe is open to the pond which is open to the air. After the pump, even if it goes into a pressurized filter both sides of the filter are still open to the air. Water wouldn't flow to and from the pond if the system weren't open.
On the other hand, if you had a valve both before and after the pump and closed both of those and water remained in the pipe and pump, that would be closed and absolutely be a huge problem. Of course the pump would also have to be off or it would burn up I think.
The issue isn't so much the ice, it's the pressure. In a closed system when the ice expands pressure builds until something breaks. When water pipes freeze and burst the burst almost always happens way inside the house far away from the ice, at weak points. Inside the house with all the fixtures closed the a pipe will freeze where it comes into the house. That ice plugs the pipe so you now have a closed system full of water. As the ice continues to expand down the pipe into the house (the diameter of an ice plug in a pipe doesn't expand) there is less and less space for the water trapped in the system, pressure builds and builds until bang.
Opening a water faucet a little will keep warmer water flowing thru a pipe and normally keep it from freezing. But when really cold the pipe can still freeze. But because the faucet is still open ice can push water out as it expands and pressure in the pipes will actually be near zero, so the trick still protects the plumbing system.
When a pond keeper understands this process, and it is surprisingly difficult to accept because we have to unlearn one of the most basic concepts we've been taught, ice in a pond becomes much less scary and very easy to manage.
Here's some links for those interested in this trivia.
http://www.weather.com/activities/homeandgarden/home/hometips/severeweather/pipefreeze_prevent.html
http://scifun.chem.wisc.edu/radio/pipefrez.html
And for those like me who like to see a small point beaten to death.
http://physics.stackexchange.com/questions/3133/why-does-frozen-water-burst-a-pipe
