The extremely delicate balance of constants and forces required to allow our protected spacetime bubble to exist is one of the reasons I believe in the Creator. Either way, something existed before our spacetime bubble began to manifest so things did not come from nothing. You may not like addressing the possibility, but it is possible that the 'ether', the gel of 'empty' space in which matter appears to exist that resists acceleration and expresses inertia may actually be due to dimension time, as in the variable of time we could call 'present'.
We are fond of saying there are three dimensions of space, yet it may be more accurate to say there are three variable expressions of dimension space ... linear, planar, volumetric. If the bang theory is accurate, the variable expressions of dimension space need not have leaped fully expressed at the instant of first manifestation. Dimension space may have progressed in complexity from point to linear to planar to volumetric. The same concept may apply to dimension time as well ... ever held a moment of past time or a moment of future time? A beam of light arrives from a distant source carrying an expression of the reality of the source at the moment of divestment for the energy of the photon. A muon (or is it a mu meson?) slams through our gravitational field and appears to stretch time such that it arrives at a time not consistent with the rate of travel prior to arrival. A neutrino ignores out gravitational field and only rarily does a neutrino interact with a mass.
It is my contention that every particle (sub-atomic actually) is compsed of a bit of energy, a bit of space, and a bit of time. Bernard Heisch contends that the virtual particle field of 'empty' space is so real in its interaction with the spacetime filed that the virtual particles amount to a real mass interaction and thus the virtual field is the cause of inertia and resistence to acceleration. I am posing one step further, that the virtual field is actually evidence of the granular nature of space (the initial point manifestation) and present time. That's all; I'm an amateur, so I can have these flights of mental fancy without endangering any 'tenure' or reputation.... But there are some very astute minds 'out there' who are coming to similar conclusion, albeit from different directions.
One must start with axioms. That is one of mine.
I do not accept your premise that there is an absolute need, either philosophical or mathematical, for there to be a "before" with respect to "our spacetime bubble". Time exists in the universe; the universe does not exist in time. Causality presupposes time, time presupposes existence (i.e., a universe). The existence of the universe cannot be contingent upon any sort of causal behavior.
Furthermore, I don't accept "fine tuning" or "specialness" arguments. Finely tuned parameters are, to me, indicators of physical principles that simply haven't been discovered yet. And "specialness" arises from our perspective: it's not that our universe is right for us, it's that we are right for our universe. Had it been different--radically different--we would have been radically different. But just the same we'd look out at it and say, "had it been any different, we couldn't be here."