Hi Neni
Please find answers as:-
1. Yes, it is very much possible based on sold to party.
How to configure:- You need to define the service and response profiles. Then you need to assign these service and response profiles to the user master data in SM_CRM->Master data then go to the particular sold to party->Service level agreement and assign those service and response profiles.
Assign all the service and response profiles to the sla determination procedure, assign that procedure to transaction type.
Define the access sequence accordingly. Please find below link it will guide you further.
SLA Management - SAP IT Service Management on SAP Solution Manager - SCN Wiki
2. You can not assign any response profile to multiple service profile, either you assign it to service product or ibase or sold to party .
3. Above configuration I had told you is very much possible without customization.
4. Yes SLA will work based on sold to party.
I hope it will resolve your query.
Thanks
Rishav