Setting up SFDC App Import for hard bounceback status

Need help in setting up a SFDC app import to pull hard bounceback status.
1. I want to understand if running this import will bring in all the contacts from SFDC to Eloqua.
2. I want the import to update only status of the contacts present in Eloqua and not bring in all the contacts from SFDC.

3. I want to understand if there are any filters/step to eliminate the import running for all the contacts in SFDC.