The grid is incapable of motion.
Are we talking about a hypothetical space or actual space? Of course you can define a rigid Euclidean space but there are other spaces you can define what the grid is capable of motion.
The grid is a mathematical depiction of distance in space.
No, the grid is a manifestation of coordinates. Distance is something else.
More formally distance between points A and B in space S is defined by a function $$d : S \times S \to \mathbb{R}^{+}$$, ie it takes in two points and returns a non-negative number defined as the distance between the points. The grid defines how you describe the points, not the distance between them. A rigid grid can have many different distances defined on it, this is why a metric space is more elaborate than just a space.
More formally again, if you have two points in N dimensional space $$\mathbf{a} = (a_{1},\ldots,a_{N})$$ and $$\mathbf{b} = (b_{1},\ldots,b_{N})$$ then we can define an infinite family of metric spaces via the $$l_{p}$$ norm, $$d_{p}(\mathbf{a},\mathbf{b}) = \left( \sum_{i=1}^{N}|a_{i}-b_{i}|^{p} \right)^{\frac{1}{p}}$$. For p=2 you get the usual Euclidean distance. And these are by no means all the possible metrics.
Distance in space is defined by light travel time.
Now you're going even further, adding in a notion of time and light and motion. Are you talking about an abstract space or actual space? If the former then you are welcome to assert anything you like, you are merely defining the space you talk about. If the latter then it is by no means true simply because you assert it.
You are trying to say it is possible that somehow if light travels in space, that it is also possible that that space could be traveling in another space at the same time. There is no other space, 3 dimensional space is all encompassing. Did you miss that part?
If you're talking about actual space then you are asserting things without justification. Why should anyone think what you're proclaiming about space is accurate? What experimental evidence do you have that 3d space is all encompassing? Although there is no evidence for extra dimensions there's no evidence against such notions. There is a difference between saying "I do not believe there are other dimensions" and "I believe there are no other dimensions". The former requires no evidence to say as it is a disbelief in a claim. The latter requires evidence since it makes a claim.
