Let's say that the number of large galaxies in the observable universe is $n$ (approximated to 350 billion).
If the universe is homogenous and isotropic, what are the estimations for the total number of large galaxies in it?
$5n$, $10n$, $50n$?
By definition, anything outside of the observable universe is unobservable. This has the annoying effect (eye twitch) of making it so we have practically no idea what the universe is actually like outside of what we can observe. We can assume that it is homogeneous and isotropic and that there are other large galaxies out there, but there is a non-zero probability that we live in a privileged area and outside of what we can observe there is nothing. There is also a chance that the universe is infinite and homogeneous. This is why Dirk said between zero and infinity, we can't observe anything about it and therefore we cannot know how many galaxies there are.
I do desperately wish there was an accurate number I could give you, but there are no estimations for the number of galaxies outside of our observable limits.
Eternal inflation posits that in the false vacuum from which our own universe inflated there may be any number of others doing the same, beyond our event horizon, all with various combinations of starting conditions and fundamental constants. It is one of the multiverse scenarios that Tegmark covers. As an aside, a multiverse can also arise from a single cyclic universe if it cycles through all possible states sequentially.
You assume homogeneous and isotropic structure. That limits the possibilities as follows: It is just as likely that there are observers at the 'edge' of our Observable Universe as there are here. Assume two exist opposite each other. They both see the same Universe we do. Repeat the argument with them. Now consider they could be in any direction. So, instead of the Observable Universe being ~93E9 ly in diameter, this new construct has a diameter proportional to the number of these observers/edges. In principle there are three possibilities: 1. The Universe is flat. 2. The Universe has spherical curvature 3. The Universe has hyperbolic curvature. All of these are consistent with a isotropic, homogeneous Universe. The Universe is flat to a very good approximation, so that if it is curved, then the curvature is not noticable with our current methods. This implies that at a minimum the Universe is several hundred times larger than the Observable Universe. So given your assumptions say that the diameter is between 1E+13 ly and ∞. My take, not that you asked, is that asking to quantify what is by definition unknowable makes as much sense as trying to figure out how many Angels can dance on the head of a pin: meaningless.