Hi,
regarding the first question I would suggest you to review this link to SAP help - http://help.sap.com/saphelp_erp60_sp/helpdata/en/d2/6f6e81415e11d182b10000e829fbfe/content.htm
regarding the next question - 'I want separate business partner number range at role level' - I'm not sure if this is possible (and even needed). as you know, the same BP might be used in different roles according to scenario applicable. so per my understanding, you have the link to the same BP over his unique ID (number), however different roles (with their codes) still allows to differentiate specific business scenarios.
Kind regards,
Renatas