This should be done in 2 stages;
First stage - User selects the import source.
Second stage - User Uploads the file(s) and waits for file processing and validations feedback. The validation responses could include the imported file preview as well.
Have a look at the 2 sample sketches below.
First Stage

Second Stage

This should be done in 2 stages;
First stage - User selects the import source.
Second stage - User Uploads the file(s) and waits for file processing and validations feedback. The validation responses could include the imported file preview as well.
Have a look at the 2 sample sketches below.
First Stage

Second Stage
