Hey rubadub
Sorry for the delay getting back to you.
1. The fish will require no hiding places in the winter, when it gets every cold they will just sit on bottom.
2. If you can raise the pump or no less than a foott from the surface, if not move to the side of the pond rather than in the middle.
3. In the winter the fish will excrete very little ammoninoa, also the bacteria will start to die off anyway due to the temperature. So you dont need to worry about the the bacteria, but i would still recommond the pump being on as when it does start to warm up theres no rush or worry about the bacteria, by leaving it on it will allow the bacteria to naturaly start.
4. Its very daft to heat a pond in my opinion, even if i was a millionaire i still wouldnt heat my pond. Instead if you can make a cover made from wish bubblewrap it will keep the temperature warm enough without a huge electrical bill.
In terms of other tips, try and provide doing any work in the pond, the last thing you want to do is disturb the fish.