APO ECC integration

Hi Gurus,

I would like to know how tightly ECC APO is integrated .

To do planning in APO DP from ECC SD we need master and transaction data .

TO do so to my knowledge SCM BI can extract the historical data and master data directly.

My question is Do I need additional BI to extract the Historical data just for the data source purpose .

If not to what extend we can use the SCM BI for its purpose.

Can it hold the historical data of what size ?

Can it still go alone without additional BI ?

If BI is in System landscape do we still need to use BI and bypass SCM BI to extract Historical and TD ?

How it will effect future integration with other business suite product if I always use SAP BI server for pulling and pushing data to ECC and other products like CRM ,SRM etc .

Please guide what is the ideal and best system lanscape for Implementing it .