1) If you choose to integrate with Community Builder or JomSocial, you can sync any DT Register field with any profile field. Then when the user logs in and goes to register for an event, all of the synced fields will auto-populate data from the profile into the registration forms.
2) You can book multiple events at one time, but there is not an automatic discount for doing this... not yet at least We plan to add that in future development though. We're always adding new things!