PA Inigo

For minimum investment, keep the ring. If you want to get actual damage out of him, I'm not sure if even raven+TA is going to cut it without a buff because you only have 49 atk at 40% advantage and most blue mages including Reinhardt will probably tank two hits if they have res in the upper 20s. Maybe if you stick a glimmer behind it, then you can squeeze out an extra 10 or so damage and that might do it.

On the other hand, you could go for that classic solution for -atk on reasonably fast mages, the good ol' blade tome. If you can collect around 12-16 points in visible buffs of which at least 4 are to atk I think you're in business. The issue is that you probably want to use desperation, which would prevent you from using WoM.

I wouldn't worry about trying to make him more useful as an attacker, since he's pretty limited there. I'd say either keep his default or give him a tome that causes debuffs to the enemy.