in physics can scale be considered a dimention?

Magnitude is not a dimension because it has no direction. It's what separates scalars from vectors.

I'm also not too pleased when people mark "time" as the fourth dimension. We can't freely move through it and it's really just a reference to events that take place.

Whatever this fourth dimension is, I doubt we can view it.

No. Scale is not a dimension. It can be a factor, certainly, but it is not a dimension. A dimension is something that is unrelated to any other thing - and scale is a factor that can be measured with height, width, breadth, weight, and so on.

Furthermore, scale is unlikely to be the biggest hurdle, unless one gets into really weird aliens (machine aliens, and so on). Consider signal propagation time along nerves, for instance. We could get computron aliens, we could get decentralized aliens (such as the dinosaurs with separate, subordinate "brains" for parts of their huge bodies), but scale alone does not constitute a dimension.

Scale is not a dimension.

If we managed to communicate with aliens, I'm sure we would exchange basic information such as simple descriptions of ourselves including sizes.

It's very easy to do this as there are convenient quantities we could use to establish length (e.g. wavelength of shortest wavelength emitted by hydrogen atoms).

There may be some larger or smaller universe, but we can never observe it. Science is defined by observation. (Schrodinger's cat is unscientific because we can't observe it. Apparently it just hurts too much to say "I don't know.")