A) Bosons don't stack. You're thinking of Fermions.

We might not see any stacking of bosons in our 4 dimensional perspective of spacetime. But can't bosons be stacked in another 5th dimension that is hidden to us, and still appear to have the same location in our 4-dimensional perspective?

This is a very interesting question. The answer is, we can tell.

Suppose you have two identical bosons trapped in an infinitely deep square well; we'll label the two dimensions of this system X and Y. The state can be summarized by two quantum numbers - the number of half-wavelengths in the X direction, and the number of half-wavelengths in the Y direction. Suppose we can only actually see the first of these - we can only measure the number of half-wavelengths in the X direction.

The interesting bit is, even if we can't tell how many half-wavelengths the two bosons have in the Y direction, if they have the same number of half-wavelengths in the X direction, we can tell if they also have the same number of half-wavelengths in the Y direction - if they're in the exact same state in

*every* dimension, that changes the statistics of any interactions.

So, adding a new dimension doesn't let you hide stacking where we can't see it. You might be able to go out of your way to create a janky theory which reproduces the effect at the cost of being much more complicated and not explaining anything new.