I am using seamless paper for the background. You need two stands and a bar for that, it is pretty large and heavy. If you go for muslin, make sure that the fabric does not show wrinkles when set up. My experience is that any irregularities on the surface will be almost impossible to hide if the background is dark and lighted. At least try before buying. With a white background, even bed sheets coming out from a drawer would be fine if it is properly lit (I did it once), but it is another story for a dark background (I tried it too with regular cheap fabric and it was a nightmare, you need to iron it).
On camera axis means along the same line that goes from the camera to the subject.