Barry,
Here is an example of how one deals with infinity which ultimately is based on a physical interpretation and isn't buried in a maze of obscure mathematics.
It is relevant to cosmology.
The curvature or flatness on the surface of a sphere equals the inverse square of its radius.
For a sphere of radius 1, the curvature is 1.
For a sphere of radius 10, the curvature is 0.01.
For a sphere of radius 100, the curvature 0.0001.
For a sphere of radius 1000, the curvature is 0.000001.
As the radius increases the surface becomes flatter and flatter.
We can make a general statement.
As the radius approaches infinity the curvature approaches 0.
Hence an infinitely large sphere has a flat surface.
When a sphere is described by its curvature its far easier to "visualize" an infinitely large sphere as simply being a flat surface.
One doesn't have to worry about what a sphere with an infinite radius looks like.
In cosmology the 2-D surface on a 3-D sphere is replaced with a 3-D spatial universe in a higher dimensional space.
Regards
Steven