my junkyard shopping list is aimed at high carbon steels for tools
axles, leaf springs and crankshafts
at the steel yard for mild steel
its a lot easier to hex or round square stock than vise versa
Id go for a selection weighted toward the larger dimesions
12" > 2" all sorts of ideas come to me when holding a larger stock
at work we make mostly architectural (stairs, railings, doors, grills ect) and use quite a lot of 58th square, Id favor it as dimensionally stout enough to draw down in places and upset in others for fireplace equipment.
most of our leaf work is 1/16" plate (laser cut) then either stamped in dies we make (40 ton sheer) or for larger leaves hand chased (air hammer), peened and curved. Contemplating doing something similar at home with hand tools Id probably opt for 18" copper plate and a jewelers saw for any complex silhouette,would be a lot of grinding and filing in steel.