Regarding point (3) above, VIRBONUS is an attested early Christian name. A quick google yielded the following examples:
 A bishop named (Saint) Virbonus, who attended the Roman Council of 595 (Source: D. Pringle: "A group of medieval towers in Tuscania" in Papers of the British school at Rome Vol. 42 (1974) pp 179-223)
 A Roman abbot named Virbonus (ca. 650) (Source: E. Wellesz: "Recent studies in western Chant" in Musical Quarterly Vol. 41 no. 2 (April 1955) pp 177-90)

I note that the Thetford treasure also has the inscription VIRBONE VIVAS. Given that all the other dedications are to persons, it seems more likely that this one is likewise, rather than the vague dedication "good man".