Super cute fabrics :-)
As for your question as big as I want to, yes I know thats no help hahahaha I tend to make them oversized 40x50 or bigger. In my experience most crib quilts are not used in the crib for very long, but can be used on the floor or couch, in the car, just to wrap up in or later on toddler beds.
If you want to make it bigger more blocks or a border or both.