The Soul thing was mainly as a replacement for the normal way to gain acts: while the other gods get acts through worship Yggdrass gets acts by adding more souls/minds to it's Hivemind, which it sacrifices again in its actions.
Since this is not his stated secondary source of power, This is not, in fact, true. Like all other gods, he gains strength through worship. You might presume that the worship gives the many minds to reproduce, of course. But the 'mechanic' remains the same. It's the way the world works.
I thought the population size should have been within a limit that the population could reproduce but if you think its too much, then lets just take 300 or 150 or something....
I will pick a number during the turn post, if you don't mind. For now, you can edit the number out. I'm going to try to keep it reasonable. Don't expect a lot of them, though. While I detest the story, I would prefer seeing an 'Adam and Eve'-style act, merely because it just seems more reasonable like that. With your natural class system, however, I'll have to up that number quite a bit. (I also don't like using too many numbers unless necessary. They complicate things.)
But to answer your question:
reduce population to 300 (or whatever seems appropriate to you, i only took one thousand to keep the genepool large enough to prevent inbreeding)
Addressed this.
reduce lifespan to 60 years. (being the first 30 years of their lives non-sentient gives them an effective lifespan of 30 years)
I can, actually, up this by a little. Let's say that they can get as old as one-hundred years. I can balance that out with high mortality rates amongst infants, as you suggested.
bring senses to human level.
It is acceptable for them to, for instance, have (far) superior smell. It does, after all, fit their origins. But, logically, I'd deem their eyesight somewhat worse, and their hearing, perhaps, equal. That is- If you are okay with that balance.
Although not stated i envisioned that of a batch of 100 young roughly 10 survive (even higher infancy mortality rates would make breeding a bit difficult since 4 Genders and all that)
High infant mortality and difficult breeding might very well balance out things a bit more.
Are you alright with the general suggestions I made?
Uhhh.
UUUUH.
IT TURNS OUT THE PHONEIX IS... something important?
There, plot solved.
What if I told you that the Phoenix is completely unimportant and I'm getting you all fuzzed up about it because I can?!