In a practical sense, I'm wondering if I should cover my walls with black material to absorb stray light.
OK, lets start at the end, you do not need to cover your walls, several things come into play, first you could simply use some black cards, as flags to block light from bouncing toward the model. Second, if you are getting a lot of light bouncing back and filling in the model when attempting to get a shadowed lighting I am going to say that you may have your lights too far from the subject and moving them closer may eliminate that effect and also create a faster falloff and more dramatic effect.
Now, I have said I use 9 lights often, I also use far more lights and have also used 1 light, so its not how many its more the placement of them. Its true that you sometimes need more than one light to accomplish something specific and at times its much easier to do with more lights than less. That all said lets get to the 2-3 light ideas.
Dark background? than you likely need to back light and have three to work with on a subject. You can use a very standard beauty light which would be one high above and one below filling in a clamshell lighting but be careful as this is what I call Fat Lighting, or flat light, why do I call it Fat lighting? it creates a beautiful glow, and the underlight that fills in the face and eyes and shadows does a great job of making the skin look good and making older models look even younger, but it also takes aways shadows and causes the face to lose some definition, so now the model needs to have a more contoured face with higher cheekbones and a more angular look to her and the make up can help by creating some contour. These are things that can be combated with lighting and shadows but this lighting style lends itself to removing those shadows and creating a fattening of the features
I am not saying that a round face is bad or good, but its something to be conscious of when using that style of lighting.
You can also use a reflector as a fill underneath, instead of a light source, its not as easily controlled but can be just as effective, you can use flat white, glossy white, silver, mirror, even a gray for differing levels of reflectivity and fill, a light source will be more controllable as you can simply set up the light and turn it on and up or down to adjust for the fill level.
Now thats not very shadowed lighting. How about a shadowy light, try a beauty dish up with grid close, maybe within 3-4 feet from the face on one side slightly at a near 45degree angle, no fill, use the modeling light to place and angle the face to get the shadows where you want them. If you need a fill you have one, as well you may want a hairlight and or background lights.
Perhaps you can add to your question and point to a few images you like so I can better direct this answer.