I'm currently in a implementation project of SAP Retail with SAP CAR, the customer has also SAP BW on HANA and SAP BO licensed and is part of the project's scope for SD, MM & FI in order to present analytical reports.
1) The customer wish to have his 7 years of historical data available for reporting. I have recommended load the historical data into SAP BW and go live with SAP CAR from the scratch. But if they wants to get some historical data in SAP CAR the way should be load the POS data into CAR using POSDTA and corporate sales into ERP (in order to get replicated to CAR through SLT Server), other option is to use Data Services to load historical sales into SAP HANA DB. It's correct?
2) My position about BW is that only should be used to keep historical data. All the analytical reports of SD, MM and FI should be performed using SAP BO as presentation layer and SAP HANA DB of CAR (with HANA Live) as repository. It's correct?
Here i have some input on your raised point.
1. I hope customer using SAP POSDM before SAP CAR ? if yes then you have to get all 7 years historic data migrated in SAP CAR.. once you have historic data in SAP CAR(HANA) then by using task you can send data to BW & BO will pick the data from HANA DB for reporting.
IMP:- about sending data ERP system it's depend on the structure..
2. I think above information will fulfill all your query..