2. No one is claiming this device is a "free energy machine".
Skeptics are, because all reactionless drives are free energy machines.
That's doublespeak. No one who believes in it claims it's a free energy machine. Ok, you are free to announce, "It's a free energy machine, therefore it can't exist!". But since you don't have any evidence to support your claim, that's meaningless. Either it works or it doesn't. If it does work, it almost certainly is not a free energy machine. No one has presented any evidence to indicate it doesn't conserve energy. If you make that claim anyway, it just shows you're making claims that aren't based on evidence. It tells us nothing about whether this device actually works or not.
It can be hard to get your head around, you may want to actually do the maths to convince yourself.
The only thing that's hard to get your head around is that you just made two assumptions that directly contradict each other. Conservation of momentum follows from Newton's laws of motion. If you assume momentum is not conserved, you aren't allowed to use Newton's laws anymore. But that's what you just did. You first assumed the existence of a phenomenon that violates Newton's laws, and then immediately started applying Newton's laws as if they were valid. If you make two assumptions that contradict each other, all your conclusions are invalid.
3. No one is claiming this device is "reactionless".
Same as above. Or to summarize:
Scientists: "Experiments indicate this device seems to work. We're not absolutely convinced yet, and we don't completely understand the mechanism. But if it really does work, we're pretty darn sure it must conserve energy and momentum."
You: "This device doesn't conserve energy or momentum. (Because, well, I just know it doesn't, even though I don't have any evidence to prove it.) Therefore it can't work."
Space doesn't work that way.
Say the device interacts with virtual particles, a la Casimir Effect. The physics of virtual particles is not analogous to regular particles. The net velocity of virtual particles is zero, regardless of the velocity of the EmDrive.
Now you're just making things up. There is no difference between "virtual" particles and "real" particles. They obey exactly the same physics. If a particle/antiparticle pair is created out of the vacuum and then is annihilated without ever being observed, we call them "virtual" particles. But while they exist, they can interact with other particles, and they interact in precisely the same way other particles do. Furthermore, that interaction can sometimes prevent them from annihilating each other, in which case we say they have become "real" particles that were created out of the vacuum by the energy of the interaction.
Actually, the whole concept of "virtual particles" is just an artifact of the mathematics: we don't know how to describe the true vacuum state, so we use perturbation theory to write an infinite series describing how it differs from another state we do know how to describe. And we call the terms in that infinite series "particles".
All of which is really completely irrelevant to the question at hand. A particle/antiparticle pair initially has zero momentum, but they absolutely can interact with other particles, and that interaction can impart momentum to them.