You haven't said what shape the pot is. You need a wider surface area than the depth of water really for fish to be happy. If your pot is not a suitable shape you can just have water plants. You also need some more oxygenating plants - they can be weighted with garden wire so they sink to the bottom. And as a minimum you need at least a gallon of water for every inch of fish.A miniature water lily can be grown in a mesh basket in special lily compost and you can put a layer of grit on top. But many water plants seem to manage without compost at all! A few ramshorn snails will help to keep the sides of the container free of algae.

My pond fish go deep during the winter months and I dont see them again till the spring, thats how they survive, so I doubt they will make it in your pot.
Your floater will sink to the bottom when it turns cold some may reappear in the spring. Aquatic soil in aquatic baskets is what you need for plants in water. You can get Collection of 7 plants suitable for a miniature pond or barrel, the ratio usually is 1 Oxygenator, 5 Marginals & 1 Floating Plant. I recommend Iris Pseudacorus and Iris Laevigata Elgar as 2 of the marginals.

Good point about overwintering - you didn't say where you live, which can affect the severity of the winter. I do know people who bring the fish into an indoor tank in winter.

Thanks for your excellant advice. On reflection perhaps fish would not be a good idea but will try some plants instead. Perhaps a solar powered fountain........?