Regarding the Ascendant/God thing, here's some good RG quotes I came across the other day that might help with the distinction (but mostly I just liked enough to record somewhere). First, regarding the Errant's fall from power:
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The Master of the Holds has walked out into the world. He is now among us. There can be no worship now-- no priests, no temples. The only blood the Errant will taste from now on is his own. . . .
And yet the whispers never went away. They echoed like ghost-winds in the god's mind. With each utterance of his name, as prayer, as curse, he could feel that tremble of power -- mocking all that he had once held in his hands, mocking the raging fires of blood sacrifice, of fervent, fearful faith. There were times, he admitted, that he knew regret. For all that he had so willingly surrendered.
Master of the Tiles, the Walker Among the Holds. But the Holds have waned, their power forgotten, buried by the passing of age upon age. And I too have faded, trapped in this fragment of land, this pathetic empire in a corner of a continent. I walked into the world...but the world has grown old. . . . Who served whom, damn you? I went out, among you, to make a difference -- so that I could deliver wisdom, whatever wisdom I possessed. I thought -- I thought you would be grateful.
But you preferred shedding blood in my name. My words just got in your way, my cries for mercy for your fellow citizens -- oh, how that enraged you. -- RG p. 238-239
The Errant talking to Fener:
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"You walked into the world."
"Not by choice, Master of the Tiles. Not like you. . . . And so my followers died -- oh, how they have died. Across half the world, their blood soaked the earth. And I could do nothing. I can do nothing."
. . .
"You have survived. For so long. How?"
"Alas," said the Errant, "my advice to you would be useless. My power quickly dissipated. It had already been terribly wounded -- the Forkul Assail's pogroms against my faithful saw to that. The thought of another failure like that one was too much...so I willingly relinquished most of what remained to me. It made me ineffectual, beyond, perhaps, this city and a modest stretch of river." -- RG p.240
So . . . okay. The main distinction between ascendency and godhood seems to be worship, I think we're all cool with that reasoning. However, I think the primary distinction is that Ascendency is personal, whereas godhood could almost be described as communal. Become a god and you don't just draw convergance, you become the support of hundreds, thousands, or more -- and they in turn can influence you. In some ways, this actually limits you even more.
It does appear that you cannot be both an Ascendant (who walks the earth) and a fully effective god (whose powers seem greatest when they remain in their own realms, where one assumes they can "touch" their followers) at the same time. Mael was greatly diminished by masquerading as Bugg, it seems; enough that Mallick Rel and the other Jhistal priests could hijack his cult and a portion of his power until Mael unveiled himself again. As Keruli, K'rul's influence was also limited largely to his immediate vicinity. The Errant's entry into the physical world seems to have crippled his own religion -- Fener's certainly did.
There does appear to be a difference between the two types of gods. While the Errant was certainly an Ascendant first, and Fener likely was an animal venerated in the same was as Togg and Fanderay, Mael is an Elder God who, by all appearances, bypassed mortality completely. As he was "born" into the position, it seems like it is more difficult for him to permanently lose power/identity because he is something of an embodiment of a primal force, not an ascended individual. K'rul was similar; though his followers dwindled to almost nothing, he was somewhat restored by resanctification (and even if he hadn't been able to influence the world, he certainly didn't cease to be -- his body basically being the warrens and all). This implies that Ascendant-Gods are more vulnerable to overthrow and loss of power than Born Gods, whatever we can take that to mean . . .
So basically, what it comes down to is a trade-off. If you Ascend there is the possibility you will become a god, but in becoming a god you will lose a certain degree of personal freedom. If, however, you refuse godhood, as Rake seemed to, you remain essentially a private individual, barring the pressure of the odd convergence.
Then again, some don't get the option of refusing godhood; Itkovian was somewhat drafted, and I somehow doubt Dassem Ultor voluntarily became Dessembrae. I guess if you're going to Ascend you should make sure you don't do it while you're a beloved public figure . . .