Would I need to ring every week? 

No, but obviously whilst learning the more opportunities you have to ring the faster progress is made. Similarly if we had a large number of ringers then with only 8 needed to ring all of the bells for a service a rota system could operate. In practice it has, however, been many years since we could regularly field 8 ringers on a Sunday so until numbers build up we would hope to see you as often as possible.