Sourcing and ATP Rule defination

We have a business requirement to create single Buy sourcing rule and assign it for each inventory organization in Assignment Set and one ATP rule with Supply Availability and ATP rule Assignment at each inventory organization. Because we have 2 lakhs plus items, and 150 plus inventory organizations and we are buying it from single supplier, so we have defined one sourcing rule buy from supplier and in assignment set we have assigned it Organization level for each inventory organization and ATP rule we have created with Supply availability and ATP rule assignment also we have assigned at organization level.