Yes. You are able to export your contacts from Central Mail and Import them into Google Apps - instructions. There is a great chance that duplicate contacts will be created, we will also give instructions on running the "Find and Merge Duplicates" tool.
Yes. Whenever you send an email message to someone, your Contact Manager adds that person's email address to your Other Contacts list. To move the contact to your My Contacts list, open the Contact Manager, click Other Contacts (at the left), select the addresses you want to add, and click Move to My Contacts.