Is Sunday a good day to visit Brugge. Are stores shops other sites open?
All the tourist/chocolate shops will be open as will some of the high end shops. It's just that some shops will not be open until say around midday. There are some also that are closed. The museums will be open, supermarkets will open sunday mornings but will be closed by 1pm, and bars and restaurants will be open. So you're good to go for a Sunday visit.
Churches that are still used as churches and have religious services Sunday morning, these might (I don't know this for sure) have modified visiting hours on Sunday, because they are having religious services.