The crux of this Imperius playstyle is to hit your Solarion's Fire in the center followed by Celestial Charge which holds them in place for Blaze of Glory's extra damage to trigger.

This engage will give you 2 charges of Valorous Brand per Hero hit and will provide a decent heal
from Battle Hunger.

Wrath of the Angiris requires hard CC to engage, since the delay is noticeable. A 15% slow from a completed Consuming Flame can help you land the Heroic if you don't have CC to followup on.

I think on 13 you can either choose Heat of Battle or Divine Rage, but you'll likely end up taking the extra healing as it can help you survive against more damage.

At 20, the focus will likely be to take Impervious to become Unstoppable and gain 75 spell armor for 2 seconds.