i have not been educated about mice, but i have a family of 8 mice that are "wild". they live in the roof of the shed and come down every dusk to be fed. they are quite unafraid of me. they start eating as soon as i place the food down.
they do not breed madly if they have no access to large food stores. there are always about 8 mice and they have been there for a few years.
anyway, i feed my mice a varied diet of mainly birdseed and sunflower seeds. i give them a small amount of grated cheese every week for their bones. they also like fresh corn on the cob, but i get the mini cobs as they struggle to drag them if they have to run off (like if a bird lands).
also, if i get a burger and do not eat all of it, i take out the beef patty and crumble it and give them that. they very much like it.
sometimes i give them grapes or little bits of bread, but that is rare.
i think it is important to give your mouse branches to climb along and pipes to run through. they like to sit inside pipes if they are scared.
my mice are expert at running through the trees and they seem to enjoy it. it gives them excersize as well.
they need hard things to gnaw (like hard shelled seeds) on otherwise their rodent teeth grow and painfully curl around.
mice dislike heat more than cold, so it is important to have a cool place for it to go to, but also provide clean and warm bedding as well.
mice are actually clean and groom themselves all the time.
i am sure it would be good to get the mouse a companion mouse. my mice are all so social and i imagine one by himself would be very sad.