Yes BIG WELCOME!!
I see no hardy winter plants that can help big time. Get some good sedges, like rushes, cat-tails, water Irises and grasses all will work good, and even better once they get growing. look for winter hardy sedges and start some up as soon as possible. Sedges are best at photosynthesis filtration.
If you have lots of fish, ensure that there is good water movement and filteration. Make sure that you are not over feeding fish... if there is left over fish food floating on the pond 2 minutes after feeding, you have over feed, that is the general rule. It is best to feed small amounts more frequently than one or two large amounts, Also if your water is cold, below 50, I would not feed the fish at all!
They won't starve, trust me!
Extra pumps and filtration may be required if current filter not keeping up.
Saw your fish pictures, you got some very nice looking KOI, lots of color! Nice floating plants last summer! Now you just need hardy pond plants that continue to clean long after the tropical floaters die off!
Here is a picture of my very large water Iris, it's a Yellow Flag Iris, and cleans very well late into the season, it takes several very hard frosts before it even thinks about dieing off....