bees do a good job at house keeping and usually clean up what needs to be done, I would think the only time to change out frames are when they get physically damaged or need to be sterilized from disease..
your second question needs more info..it depends on how many bees are in a colony on how much food they need...if you have 4-5 boxes full of bees going into the winter, I would aire on the side of precaution and leave extra food than short them and have them starve, also making fondant to feed during the winter is always a good idea...this is one case of more is better..because in the ice cold you cant open a hive to check for honey stores..
