Don't really understand this: would my first call include marker as empty string:

/object/billing/namespace/{namespace_name}/info?marker=""&include_bucket_detail= &sizeunit=

Or, would it just omit it?

/object/billing/namespace/{namespace_name}/info?include_bucket_detail= &sizeunit=

On you first call, the marker querystring will be empty.  However, you will notice in the response (of the firs call) that a value is returned in a field called next_marker.  Pass the next_marker value as your marker in subsequent requests to continue traversing the list.

-Ben

You can just omit the marker querystring on your first call as this field is optional.

-Ben