That all looks legitimate. On a crit, you reroll all dice, so Divine Smite fits right in there. Your right about Savage Attacks, and correctly applied the 1d6 (this is why half-orcs may favour greataxes with that 1d12).
Now, that's totally OP damage, given that the creature only had 20 hps, but man you gotta give Nar the slow clap on that one.