Question about container size

[2Tranquil]

I just had this lovely pond setup this summer and now that winter is approaching ... I'm not sure what I should do with my fish & plants.

I thought I could winterize it outside, but from other postings I've read I think I'm going to have to bring my stuff indoors (but I'm not sure.) If I bring them inside, what gallon size container would be best? Which plants do I need to bring in?

My out-door pond is pre-formed, 2 containers with a connecting section between them. Overall it's 155gal. (at least that's what the container labels added up to) but only 18" deep with 6" plants shelf around perimeter, with a fountain pump. I have 5 butterfly koi & 6 comet fish, hardy lillies, miniature cattail, Bluebell & an Iris I'm worried about. I think I'm in the planting zone 4 or 5 - it does get pretty cold.

Would I need to bring them in? What size container? Can I leave them outside with a floating de-icer & keep the pump running?

Thanks!