Food size depends on the size of the particular snake in question. Generally, try to feed your snake a food item equal to or a bit larger than the snakes largest part, i.e. 1 1/4 the size of the snake's body (girth). I feed mine every four days, but anywhere from 2-7 days is what I've read.
Clean the cage when it's dirty and do a full cleaning. Change the substrate, wash the container, water dish/bowl and furnishings with anti-bacterial soap and warm water. It is not highly recommended to use a bleach solution greater than 5% and even at that concentration, rinse, rinse and rinse. Your choice of substarte either makes it very easy and quick to do a cleaning, or a little bit more time consuming. It's your choise though.
I hope this answered your questions. Outside of writing my own care sheet, there's not much more I can say. The care sheet links above cover all the basics and should give you a good starting point.
Good luck
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