Hi Anukaran,
Once replicating in BI system, you have to change/edit the datasource and activate it.
1. After this, when you initiate full/init the data gets into PSA.
2. Yes, after your datasource and target(CUBE/DSO) is ready then you have to do transformations between them(mapping source fields and target info objects).
Once mapping is completed, you have to create DTP'S for CUBE. So, when ever you execute this DTP, the data gets triggered from PSA to target(CUBE).
3. No, it won't.
Thanks,
B V Sagar.