In your analogy, and I can't stress that it is an analogy enough, the surface of the balloon is representing 3d space. We don't see the interior of the balloon because it's not the universe it's the shape that the universe is curved around.

What we actually observe is that distances on a cosmic scale are all getting longer at a range proportional to their length. This is distinct in some ways from observing objects moving away from us, specifically it isn't restricted by the speed of light as the objects don't really have the velocity that the changing distance to them implies.

Apologies, relativity is quite hard to explain especially without diagrams. The answer to your other questions is that it is reality that is stretching, the distance between two galaxies becomes larger rather than one of the two galaxies moving into a new space. So it's not limited by the speed of light.

As for your questions about the fastest two things can move away from each other, that's actually a more complicated question than you realise. The issue here is that the maximum speed anything can be observed to be moving at is the speed of light. If you took two objects moving away from you at 0.75c (0.75 times the speed of light) then from the perspective of one of those objects the other wouldn't be moving at 1.5c. Instead it would be moving at 0.96c, and you would notice that clocks on the objects no longer match yours.

From the perspective of relativity, everything is always moving at a constant speed through space-time from every perspective. The faster something is moving through space, the slower it is moving through time and vice versa. Light speed is achieved when an object has no mass, resulting in it travelling entirely through space and experiencing no time passing. There's a whole bunch of effects that result from this like length contraction and time dilation.

Space expansion is very different, It has nothing to do with the object you are observing, it is instead a property of the space between you and the object. In a sense neither object has relative motion, instead the ruler you are using to measure the distance between the two is changing it's length.

The speed of light is how fast an object can move through space, but the universe isn't expanding by motion, it's expanding by changing the size of space. To us an analogy, consider a balloon with objects on its surface. The speed of light is how fast objects can travel across the surface of the balloon, but if the balloon is inflated then the distance between two objects can change faster than that speed.