Unintuitive concepts- boundless finite universe etc

Hi
This is kind of a brain fart post.

The idea that the universe is both boundless and finite intrigues me. For some reason i only realised this concept recently.
I know it can be understood in terms of the concept of a boundless finite space in 2D- ie the finite surface of a sphere being 2D but being boundless because of its arrangement in 3D space.

But its odd how by just going up a dimension, it becomes hard to imagine and unintuitive. So what is the fourth dimension that confers boundlessness on a finite 3D space universe. Is it time?
If it is how does it do this.

I got caught up thinking about this yesterday. Thinking about the analogies that can be drawn between 2D/3D/4D etc.
eg if you intersect 2 of these boundless finite spaces (sphere surface) you can get a circle (2D) or a point (1D) obviously.
So what happens if you take it up a dimension and intersect 2 boundless finite universes. Are you going from 4D to pure 3D or something (or even 2D). Would the intersection be pure space/plane without time. Or some other variant.

As i say, i'm just wondering about this (no university physics background) but this concept has intrigued me. Dunno if it's directly relevant to physics, but anyone know anything about this stuff and some basic stuff i could read about.

Also, something else that intrigues me.
There are distant parts of the universe that other parts of the universe have never seen (ie speed of light being a constant, the universe only existing for a finite time and the space between the two points being the greater than universe's age times this space). Can someone tell me. Is it possible that such 2 points of the universe may never see each other no matter how long the universe exists.
I know the concept of light cones and causality are somehow relevant here (if they are can someone explain this to me ). But that thing about 2 points in the universe "never having anything to do with each other"- is this possible. And if so, what are the implications of this. If so they may as well be in different dimensions.

Again, is there any basic reading you could suggest to understand this stuff. I appreciate the above is not very coherent. But maybe someone will get what i'm getting at.
Thanks.