I think it is sufficient to run front-end. Just keep in mind you need a big enough /var/tmp for Sunstone (uploading images and converting them to the datastore of choice). In my case (oned+sunstone+CEPH bridge) I need at least three times as big /var/tmp as the largest VM image you will ever want to upload.
Anyway, does anybody know whether it is possible to download images from Sunstone?