So just to make sure I'm understanding those things correctly:
World Level doesn't matter at all, so it can be ignored. To upgrade Essense, you need to breed a higher stat level in to a race. Say, breed a C level Libido in to a Thriae, and then C level Fertility, and then C level Aptitude. After that I offer up each Thriae with the C stats to the Emissary to upgrade them from common to uncommon in the spawning area, correct?
Yeah world level or focus in increase essence level, really dont care, if wanna get higher Nephs, best way is at the farm, you can use Nephs talking to the Emissary for increase level, but non sense that when you can level up essence at the farm, when you get a legendary at demons, titans or whatever that will make automatically level 5 essence, but that willnot affect really to the wild nephs, you can lost time waiting wild nephs that never will find one more than rare, i dont remember saw a epic or legendary wild even when i liberated legendary nephs so like i said best is mix nephs with the best traits for xp, lust, etc
Also forget about rank for xd i never caressed about, just breed nephs with same traits and will level up to 5 directly when you get a legendary