Yes, living people are automatically marked as private in GEDCOM processing. This assumes that we know they are living. Sometimes there are no dates in the file and the person isn't related to anyone living. To guard against these cases it's important to click over to the one-page Privacy Changes tool to review the privacy settings after the import. The link to this form will be in the e-mail you get when the file is processed.
Non-living people are set as public, unless they're nuclear relatives of living people.
For the other questions, see the help pages on Trusted Lists, etc.
For more on GEDCOMs, see the GEDCOM FAQ.