What are the user privileges required to for an ssrs report owner to ‘send email’

You need to use Credentials:

A credential is a record that contains the authentication information (credentials) required to connect to a resource outside SQL Server. This information is used internally by SQL Server. Most credentials contain a Windows user name and password.

The information stored in a credential enables a user who has connected to SQL Server by way of SQL Server Authentication to access resources outside the server instance. When the external resource is Windows, the user is authenticated as the Windows user specified in the credential.

This way you can associate your SQL login that sends the mail with an NT credential that has file access to the attachment.

There is no need to grant the CONNECT role. In 10.2, Oracle finally reduced the set of privileges assigned to that role to just CREATE SESSION but in previous versions, that role has many more privileges than the name would imply.

It would be more secure to create one users-- one that owns the tables, procedures, etc. but that does not have CREATE SESSION privileges and one that has appropriate privileges on the various objects that the application can use to connect to the database. That allows you to do things like prevent the application user from dropping tables or from deleting data from logging tables.

Additionally, the owner of the tables is going to need to be granted quota on whatever tablespace or tablespaces that user's tables are going to be created in. You could grant the owner the UNLIMITED TABLESPACE privilege but it is more secure to grant them a smaller quota on whatever tablespaces they actually need to use.