i would base those decisions on the type/style quilts you make...do you use alot of fat quarters? or jelly rolls? are charm squares your favorites?
determine what sizes are your- go to if you were to go purchase pre-cuts & work within those sizes. a person who does alot of water-color quilts may cut all their fabrics into 2" squares...someone who loves turning 20's, yellow brick road type quilts may want stacks of fat quarters to grab...only you know what you are most apt to make use of.
remember you may want to save some yardage for border fabrics too.