10.What are the best practices we can follow in a BW system?
 
Best practices for a production BW system can be drafted only with a close interaction with the functional team and technical team and the nature of the production system.

Here, are couple of best practices we could implement to improve the performance. 
Activate Transfer rule for info source:When you have maintained the transfer structure and the communication structure, you can use the transfer rules to determine how the transfer structure fields are to be assigned to the communication structure InfoObjects. You can arrange for a 1:1 assignment. But you can also fill InfoObjects using routines or constants.
Use scheduler:
The scheduler is the connecting link between the source systems and the SAP Business Information Warehouse. Using the scheduler you can determine when and from which InfoSource, DataSource, and source system, data (transaction data, master data, texts or hierarchies) is requested and updated.
The principle behind the scheduler relates to the functions of SAP background jobs. The data request can be scheduled either straight away or it can be scheduled with a background job and started automatically at a later point in time. We get to the data request via the Scheduler in the Administration Workbench Modeling, by choosing InfoSource Tree ® Your Application Component ® InfoSources ®  Source System ® Context Menu ® Create InfoPackage
 
Assign several info sources: Assign several DataSources to one InfoSource, if you want to gather data from different sources into a single InfoSource. This is used, for example, if data from different IBUs that logically belongs together is grouped together in BW.
The fields for a DataSource are assigned to InfoObjects in BW. This assignment takes place in the same way in the transfer rules maintenance.