MN is enough for healing.
Mits will make it risky to stack blue.
Joon as a monk is very durable and more emblemmed than Poseidon.
Ursena will make it risky to stack yellow.
Vela will make it risky to stack red.
I like aoe better for war defense, your team will often survive with holes. you want to compensate with aoe when possible.
Unfortunately, yellow is your worst color for center units but I think my recommended team will do you good during round 2. in round 1, you’ll be monopurpled and no lineup will matter. in round 2, the attacker will need to green on you, which is a more expensive color to have good heroes in.