A) I hope you do not stop all feeding at the end of the season. Just because you have stopped shooting, that does not mean that surviving game has stopped eating. Your birds have developed a dependency on you, and you should keep some hoppers going until the birds stop using them.
As far as your rat problem is concerned, it is important to lay down poison at each hopper site, and to keep the poison topped up until it is obvious that it is no longer being taken. Take great care to use the poison responsibly in correct bait stations, observing all the accompanying instructions and taking special care not to kill non-target species. Hoppers and maize covercrops provide a plentiful food supply for rats, but they also concentrate them into small areas, where a thorough poisoning programme will deal with them.