I think Sev is not short for Severus; it's short for Sebastos, which is the Greek equivalent of Augustus.
I really don't know - his name was Opelius Severus Macrinus , maybe someone can jump in and clarify this?
Close. AVT (autokrator) K (Kaisar) OΠEΛ (Opellius) CEV (Severus) MAKPEINOC (Macrinus) K (Kaisar) M (Marcus) OΠEΛ(Opellius) ANTΩNEINOC (Antoninus).
No, but there's only so much room for an inscription on the flan. Something had to be omitted, I guess.