Bulk Upload Interface and Flow

I have a bunch of desktop applications that do bulk uploads (they allow users to upload data from a spreadsheet into a database). The bulk upload programs do data validation, as incorrect data being uploaded would be costly to the business.

If there are any errors in the user's file, the program reports the errors and makes the user fix the errors before being able to proceed with the upload.

Question 1: Should the bulk upload program stop the user from proceeding until the errors are fixed, or should it automatically proceed with the upload but only with the valid rows?

Question 2: The users have asked for a new feature -- warnings. So these are things that shouldn't stop a user from proceeding but things that the user should be aware of before proceeding. Should I force the user to acknowledge the warnings before proceeding, or should I just show the warnings and allow the user to proceed without any friction?

Question 3: Should I display warnings and errors in the same grid, or should the warnings and errors be displayed in different grids?