“The surface of a sphere may be two dimensional, but the sphere itself is three. Just sayin’.”

A curved surface doesn’t need another dimension to curve into. I didn’t write about a sphere, I wrote about a specific curved plane which can be represented as a sphere surface. I did that because it is difficult to figure a 3D curved space.

A am not a physicist, but I don’t think Einstein used a 4th spacial dimension when writing about the curvature of the space/time that a mass provokes… Just sayin’.

The example was to point out that not every kind of space can have boundaries. As far as I know, the visible (to us) universe doesn’t seem to be particularly curved. So the question about the universe boundaries make sense (at least to me).

Regarding KISS and other dimensions you are being a bit naive. Keeping in mind I am not a physicist, what I know is that in order to explain some measured phenomena, scientists have developed some theories. None of these theories manage to explain those phenomena with 3 dimensions at the moment. They may develop another theory where 3 dimensions are enough. Anyway they try to be KISS…