It is important to clarify that the expansion of the universe is not governed by objects moving through space but rather by the expansion of space itself. This expansion is not limited by the speed of light. While objects within the universe, such as galaxies, have relative velocities limited by the speed of light, the expansion of space between objects can cause the distance between them to increase at speeds greater than the speed of light. However, it's crucial to understand that this does not violate the laws of physics, as the expansion of space itself is not subject to the same restrictions as objects moving within space.
Regarding the concept of a boundary to expansion or a limit to the size of the universe, current scientific understanding does not suggest a boundary in the sense of a physical edge beyond which the universe does not expand. Instead, the leading theory suggests that the universe is infinite in its extent. However, the presence of dark energy, which is a theoretical form of energy responsible for the accelerated expansion of the universe, does play a role in shaping the expansion dynamics. Dark energy is thought to permeate space uniformly and may continue to drive the expansion indefinitely. It's worth noting that dark energy and dark matter are distinct concepts. Dark matter refers to an invisible form of matter that interacts gravitationally but does not emit or absorb light, while dark energy represents a hypothetical form of energy associated with the acceleration of the universe's expansion.