Just to reinforce my point above about how absolutely critical is, look at the rules for how a Mythos works
Mythos: So long as he is performing something related to an Aspect of all 3 Archetypes of his Mythos, successes from rolls of all action gain a (x8), for an Aspect related to at least two Archetypes of his Mythos, successes from rolls of all action gain a (x6) and for all actions not related to his Mythos successes from rolls of all action gain a (x4).
Three Archetypes: +x4 multiplier compared to base
Two Archetypes: +x2 multiplier compared to base
One Archetype: No effect at all
Note this is a big limitation, as he only has one aspect for each of his archetypes, making him much, much less flexible than Lorgar. That means we need to be much more careful now
@DragonParadox, I do like the idea of Rebirth, but it may be that I'm missing something and you see lots of scenarios where we'll be making Physical rolls where Rebirth, Speed, and Rebel all apply, or at least two of them apply? I can't really see many scenarios where he'd be making a physical roll and rebirth would apply as he can't get Mythos powers. If he could things would be different, but as is…
It seems that in the scenarios we face (war and more war, something like the combination of Purge, Destruction, and Rebel would be more likely to have multiple archetypes trigger on Physical rolls, as he's a Physical primary demigod.