1) To begin with, space or the interstellar medium if that is what you are refering to, accounts for all the matter that is not in stars, neither in planets or asteroids, and there is actually a lot of matter in there.
However, from an human point of view it is legitimate to consider that space is "empty", given that the average density of particles is tremendously lower than what you experiment on Earth. For example, physicists who try to obtain the emptiest environment for their ground based experiments manage to go down to millions of molecules per cubic centimeters, which you have to compare with average densities of tens of molecules per cubic centimeters in interstellar atomic gas clouds. This is a whole different level of emptiness.
So, if you were to take a human-sized "cube volume of space outside the ISS", indeed you would observe a very little amount of molecules (like carbon monoxide or dihydrogen), atoms (like hydrogen), ions, electrons, dust particles, some cosmic rays but also photons and neutrinos.
On one hand, the number of neutrinos and photons that would be crossing your cube at each seconds is nowhere near negligible, as the flux of these guys is very important everywhere in the universe, mainly due to the thermal emission from stars and from the ubiquitous cosmic microwave background.
On the other hand, you are right when you guess that the amount of baryonic matter contained in that cube would be ridiculous, but this is by no mean negligible if you start to consider a cube of $1 \times 1 \times 1~\mathrm{pc}$, where $\mathrm{pc}$ stands for parsec, with $1~\mathrm{pc} \approx 3,1 \cdot 10^{16}~\mathrm{m}$.
In a cube this size, assuming a density of 10 molecules of hydrogen per cubic centimeters this would add up to a total mass of hydrogen of the order of $10^{23}~\mathrm{kg}$, which is close to the mass of Mars or Pluton. Now, realize that there are many interstellar clouds which sizes range from sub-parsec to hundreds of parsecs, with densities ranging from tens of atoms per cubic centimeters to $10^7$ molecules per cubic centimeters for the densest molecular clouds. This is a lot of matter, actually way more than what you find in planets and stars.
What I wanted to demonstrate here is that if the universe may appear filled with emptiness, it is important to notice that when you sum up things, you find out that most of the mass is contained in these vast and apparently empty spaces.
For that reason, the statement that "space is not a complete vacuum and it's full of plasma / matter" makes sense. I would just add that it is also massively filled with photons.
2) Concerning the "plasma is everywhere" statement, this can be considered somewhat true as well. Let's return to the definition of plasma. According to google, plasma is "an ionized gas consisting of positive ions and free electrons".
Let's make a list of a few astronomical objects which are in a moderate or highly ionized state:
That already represents a large portion of what is found in space. In fact, all things considered by using a rough estimate you can show that up to $99,9~\%$ of the observable universe is made up of plasma.
3) About the "electric universe", I won't comment as this statement sounds a bit vague to me.
