The universe appearing to expanding faster than c is not at all the same thing as gravity propagating faster than c.
c is a constant of travel through space-time, not a constraint on space-time itself. Extremely rapid increases in the dimensions of space don't change c or anything dependent on c.
There is no evidence to suggest that gravity can propagate faster than c, but we will likely have to wait for a relatively nearby supernova to have solid empirical verification.
Gravity and space-time are interchangeable as theory holds. But, we don't know what space-time is. Funny thing we don't know what gravity is then, either, by proxy (and reality). But, as far as general relativity is concerned, it is simply a curvature of space-time.
One of these days we'll understand what nothing is.
And yes, you're right about C. But, commonly people confuse it. I've seen plenty an argument try and entangle C with gravity/space-time and it is a shameful tactic.