1. - correct. Hidden fields are still in the data unless you choose to extract and aggregate by the fields in the view.
2. - are you using a Union to bring all of these files into Tableau at one time? Using a wildcard union to bring them all in would allow you to hide or remove the data fields from import in one move and any new files dropped into the same directory would be imported on the next open. Help covering this topic: Union Your Data
3 - Not sure you need to use blending and I wouldn't recommend it unless there is a specific use case for it.. These sound like csv files of data that are for different time periods but with the same fields in which case the wildcard union is a great way to manage them.
I hope that helps
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