Cost elements are the CO equivalent of G/L accounts in FI.
PS does not dictate nor define cost elements, the accounts will come from the FICO team. Account determination comes from many places in SAP including purchasing, inventory management, finance, internal controlling. internal labor costing, etc. PS has to be set up to handle all of the cost elements which can post to a PS object.
Cost Center usage comes from the CO team and how the business is organized.