One Database or two?
Should work fine. Best practice is definitely two databases. 

IMHO it is easier to understand where data is stored and deal with update and rolling back changes when the databases are separate, but in some hosting environments you are forced to use a single database for both the Drupal and CiviCRM tables.

Using separate databases requires you to go to CiviCRM > Administer > System Settings > CMS Integration and copy the array generated to your Drupal settings.php file.