Hi,
Reg. your question 1, the problem is you are loading from 0MAT_SALES_ATTR to 0MATERIAL. The former has a granularity of Sales Org and Material (because Sales Org is compounded) which is more detailed than the latter which has a granularity of only Material. You are bound to have duplicate records here.
There should be a business logic to determine which of the duplicate records should be loaded to 0MATERIAL. Please check the TRFN for this. If you don't have such a logic, then you need to identify such a logic (maybe with the help of functional guys) and implement it in the transformation.
Reg Q2, as others have pointed out you need to check the customer exit code for the datasource. Take an ABAPper's help if needed.
Regards,
Suhas