typically till ehp6 we recommend 70 employees for optimum performance
of course OADP Buffer is available from SP10 ie HCM FP3. http://help.sap.com/erp_hcm_ias_2012_01/helpdata/EN/37/878a840ff940b6b12382485e720bd7/content.htmhttp://scn.sap.com/community/erp/hcm/employee-self-service/blog/2013/04/25/manager-self-service-mss--performance-optimization-with-oadp%20-%20#rpctoken=1431050525&forcesecure=1 now coming to see the employees under sub org units, you can do via List view and manager needs to have structural authorization to see all the subordinates as well, typically we deliver standard rules and paths which show the employees automatically, for restriction and tweakin refer this wiki http://wiki.scn.sap.com/wiki/pages/viewpage.action?pageId=190743879