I totally missed that Lightsworn can put out decrease atk, I just had his increase def and revive in mind. I would change my team recommendation, use him instead of Rearguard Sergeant. Especially, as he is allready rank 6 and she is not. Vogoth, Lightsworn, Athel, Skullcrusher, Aothar.
But before he can really improve your team, you should visit the Minotaur. All champs need Warmaster/Giantslayer. When Apo leaves the team, leech is the only healing the team has. The extra damage from tier 6 masteries can leech health, absolutely necessary to stay alive.
On the long run, Athel will leave the team next, but for now, it will work. Later on, maybe Scabrius may take her job (weaken) and Vogoth's part (leech) at the same time and you could add Ronda. But don't try to many changes at once, complete Lightsworn (Minotaur, Ascension) first.
For speeds: Just test it. Watch the first rounds of the fight. If they are in an 1 : 1 order to the CB, everything is ok. All 5 of your champs go, then the CB gets a turn, all 5 of your champs go, the CB gets a turn...
Stun target: The CB will prefer to stun champs of weak affinity. If there are none of these (if you fight him at void stage, for example), he will take the team order into account and prefers to stun the team leader. If you want Vogoth to be the stun target, put him as team leader. His aura is for all battles, so you would get a small benefit from that on top.