this is the set-up they are in now

Amanda, I would think your fish might be fine. Air temperature as related to ponds and lakes is typically cooler (water takes longer to cool). However, since your goldfish are above ground level, it's recommended you take the temperature of the water when it cools down. You can use a digital cooking thermometer if you've got one. When water stays at or around 50 F, you need to stop feeding your fish. They will go into a type of hibernation mode, and food would be bad for them. If you feel you can't keep the waterfall going due to colder temps, you will need to add some aeration - aeration stones work well. For your climate, I think that's pretty much all you'll need to do. I would not stress them (no touching or handling either as it will remove their slime coat), nor feed them until the water temps go back up above 50 F, then feed them only as much as they'll eat. Any plants that will die should be removed as they will decay and use up the oxygen your fish need. Any plants that can survive your temperatures will be fine for your fish - those that need trimming back and/or lowered should be taken care of at the 50 F. mark.

I live in an area where the temps get much colder, and our small pond is in the ground. I will stop our pump and waterfalls as they won't take the freezing temps, and stop feeding my fish at 50 F. I have aeration stones already, but will add a pond warming rock/de-icer (just a portable warmer for ponds). I doubt at 50 F air temp, you'll need the pond warmer. If in doubt, you can add aeration stones for added oxygen.

The above advice is pretty good. Just be careful even if the temp doesn't go below 50F, what you want to avoid is the fluctuations possible at that temperature. That is the temp of torpor which is kind of like hibernation. Going in and out of hibernation is a stress to your fish. Stress leads to a compromised immune system. There is good info on this in this article Keep Your Pond Fish Healthy In Winter

You said the temp on your winterized porch never goes below 50...but what about the temp they are in now? Are they in the winterized porch? I might have missed that... They can withstand a lot of cold but mine are at least 26" below ground in zone 5 I have an bubbler/air stone with filter placed in garage with hoses i use year round and turn the falls and filter off in the winter because they will freeze. The goldfish have been fine for years! First year I was afraid for them and what a mess trying to catch them all!!! But we did and we put them in an aquarium. It was nice seeing them but they have been happier staying in the pond for several years now