Tabletop, Yes, see above, and see above.
Good idea. Carron's last melee upgrade in SS is a Khornate Chainaxe, but the chainaxe is a close combat weapon in TT, so I think Iron Lore grossly overestimated its power.
I bet I could work in the Daemon Prince idea, too; perhaps once no enemy Rhinos remain on the field, Carron could transform into a Daemon Prince, or I could attach a numeric limit to the number of Rhinos he has to destroy. Either way, it would probably accompany an increase in points cost.