Templating the bucket name doesn’t work, perhaps it might work in the future, but the bucket itself must be in the query itself in order to determine which indexes will be scanned when using the query.
As far as the query timeout is concerned, you can use the n1ql_timeout (http://pythonhosted.org/couchbase/api/couchbase.html#couchbase.bucket.Bucket.n1ql_timeout) to adjust the timeout. Indeed the default is 75 seconds.
The problem with handling large amounts of data in the client is the timeout value. The typical use case is small timeout and small operations (retrieving single items); for which the timeout defaults to 2.5; the client can certainly handle larger amounts of data, but the user needs to take care of setting the timeout appropriately. On the other hand, MySQL has very high timeout settings.