Stoicism without Stoic Cosmology

Recently I had a conversation with Kai Whiting, a philosopher and professor of Stoicism in the UK where during, and I mean for nearly the entirety of the conversation, we talked about the Stoic god. I'm an atheist, this is well-established at this point, and something in particular about Kai's views caught my attention, and that was this: That the Stoics believed the highest only good was a virtuous character and, in order to be a Stoic, one had to believe this. As this belief is informed by the Stoic's cosmology, one must believe in the Stoic conception of god in order to believe that virtue is the only good. Ipso facto: you maintain a coherent and logically defensible Stoic practice without believing in the Stoic god.

My immediate inward-facing response was, to quote Tim Urban, "Wait, but why?"

I don't yet have all my thoughts together on this but I wanted to "put to paper" what thoughts I have at the moment--unorganized and partial as they may be.

Did the Stoics ever claim objective truth?

I'll start with what I'm most curious to figure out: when the Stoics put forth their Cosmology, was it as fact or was it as opinion? Did the Stoic's claim the Stoic god objectively existed or was their god simply a means to a start? Or a theory?

If it was a theory, what's to stop us from moving the starting point of adoption (of Stoicism) forward one step from necessary belief in a conscious cosmos to necessary belief in the subjective claim that Virtue is the only good?

What is the concept of god at its core?

A theist would say that god objectively exists. Were you to ask a theist who created this god, that theist would respond, "Nothing. God has simply always been." So then, at its core, what is the fundamental essence of god (or, if you prefer, of God)?

Is it not simply a point beyond which you accept the rest on faith? 

If this is the case, if "god" is simply a point of demarcation between what can be empirically proven and what one chooses to accept on faith, why must it be required of a practitioner of Stoicism to make their leap of faith at point X rather than point Y? Why is it required to believe in the Stoic god rather than simply believe that Virtue is the only good? 

What Stoic claim prevents us from redefining god without "breaking" Stoicism?

Why can't we change the ancient Stoic definition of "god" from a conscious cosmos to the phenomena of Virtue? Why can't we stop there and say the leap of faith necessary is to accept that Virtue is the only good? Full stop. Why, if we don't need to prove the logical existence of god, do we need to prove the logical belief in Virtue being the only good?

I'm not as well read as Kai, I've not had the same amount of exposure to the ancient texts of Stoicism and I don't read Koine Greek, nor Latin, nor ancient Greek, thus I have significant limitations in setting out to answer this last question but, here it is:

Where in ancient Stoicism is there an argument made that prevents us, doing as I've describe above, from severing the cosmological connection without breaking Stoicism?

And here I'll think of my new friend, Keiran Setiya, who reminded me in our conversation last month that, "Argumentation has its limits."

I've got plenty to think about, and I'm happy to hear your thoughts below.