1. Avast Free is enough for private use. If you want you can use a Firewall-Program with Avast together.
  2. A quick Scan every week is enough. Can be sceduled in Scan Settings.
  3. It updates automatically via stream updates every few minutes and database updates 2-4 times a day.
  4. Thats absolutely safe.
  5. No need to do that. But good if youre encountering a false positive or an undetected malware sample. (Mail is virus@avast.com)