Would an 8 Essence Archangel-Emperor of Mankind work? (I'm calling him that because it sounds better than Warrior Angel-Emperor of Mankind.)
Realistically, the warrior angel and Tykki are unique units and would be counted as archangels for all but the richest of gods. Additionally, Tykki was designed by a god of weapons, so combat-wise, Tykki is probably near-unbeatable even by other archangels. As the god of humans, your Emperor will likely be more focused on leadership ability than close combat.
What is a 4 Essence generic aligned angel capable of doing? Can I get a discount if I make a bunch of them in bulk?
The majority of the 4 Essence cost is for the design of the angel. Once you have a prototype, buying up more is quite cheap. Note that you cannot buy up bulk amounts of unique-labeled units (and neither can the other gods).
Just to paint a clearer picture, do you watch Supernatural? On another note, one of the weaker archangels in the series blacked out the entire Eastern (USA) seaboard just by appearing. I'm guessing that he would count as the Messanger/Warrior angel you mentioned.
No, but I may read the Tropes page if I find some time.
EDIT: What's attunement?
It is a permanent boost in a specific class of magic. I believe currently, your options are celestial, elemental, psymental, ritual, enchantin, musical, cosmic, dimensional, universal, and eldritch.
EDIT2: Is there any way to increase max Essence?
Yes. Every turn when your projected Essence exceeds your current Essence capacity, you have a chance of increasing Essence capacity. The larger your Essence income, the greater the chance (and amount).