Frank Merton said:
I'm not sure what point you are trying to make, but I do see one big mistake -- you treat infinity as a number that one adds to and subtracts from. Infinity means endless, so it is not a number. If anything about the universe is infinite, then it is infinite, and you can add another similarly infinite universe to it and it has not gotten any "bigger."
My point of everything already existing is that, in an infinite universe, infinite time must have elapsed for this infinity to exist. Taking this into consideration, an infinite universe must already exist. If new universes are continually being created, time is also continually being created, so the universe cannot be infinite. This is Immanuel Kant's objection to the idea of infinite space.
Are we not considering an infinite 'number' of universes? Is there Infinity in the abstract? If infinity means 'endless', endless what? There can exist 'endlessness' without it being infinite. For instance, space may be finite but unbounded. In this case, the universe may appear to be endless, but it is not infinite. The surface of a sphere is like this.
Now, how many points can we mark on the surface of this sphere? Theoretically and infinite number. But if our 3-dimensional universe is an extension of the 2-dimensional sphere, there can only be a finite number of points - elementary particles, stars, galaxies - that can be placed on the 2- dimensional sphere's surface or within the 3-dimensional spacial volume.
So, in the above case, the universe would appear infinite but would always contain a finite number of universes.
I don't know if the universe is infinite or not or whether our 3-dimensional space is finite but unbounded - enfolded in a 4-dimensional hypersphere - or whatever. You are right that an infinity cannot be added to or subtracted from. But as new universes are constantly being added to a multi-verse, in this sense this kind of universe cannot be infinite. It can only be infinite if its infinity is already 'complete'. If all time and all space already exist as this infinity.
Thinking in this way, the past and the future already exist in the same way as the present exists. Everything has already happened. Our human perception as the past as memory and the future as as not yet realized is only an illusion created by the human mind.