Some friends who do portraits, weddings, etc. I have been told that most of the "magic of the photo" is actually only handled in Photoshop, and how the camera is actually used, and the camera is not the only thing to think about.
While a slight image processing is needed to correct white balance, colors, exposure, etc., it would slightly disagree that most of the "magic of the photo" is found in Photoshop.
But I do agree that the camera is not the only thing to think about. Much more important than the camera are the lens and lighting.
Nikon D3000 has about 10 megapixels. There are many portraits if you frame the image to take advantage of all those pixels, although as of 2019, even entry-level cameras offer more. It has 11 focus points, which could limit it more than its 10 megapixels. Like DSLR, it lacks eye autofocus. Its flash sync speed is 1/200 s.
If you are looking for an entry level portrait camera today (2019), I would recommend an entry level mirrorless camera because they have a lot of AF + AF eye points and because they focus using the main image sensor, so they virtually guarantee Accurate and consistent approach even with third-party lenses.
To take good portrait photos with a camera with a clipping sensor, I would recommend adding at least one 50mm f / 1.8 lens (they are good value for money), maybe an 85mm f / 1.8 lens, at least one Flash or two with appropriate flash brackets and light modifiers such as umbrellas, and some means to remotely activate those flashes. If you take pictures in sunlight using a flash, add a 4-stop ND filter due to the flash sync speed of 1/200 s (sunlight + flash + wide aperture requires an ND filter or shutter speed higher; the latter means high -synchronization of speed that "wastes" part of the output power of the flash).
If using a full-frame camera, select the 85mm lens but consider replacing the 50mm lens with a 135mm lens if you can afford it. Of course, this does not mean that 50 mm is particularly bad for full-frame portraits; It only requires a short working distance to fill the frame, and a short distance slightly distorts the face. However, if instead of emphasizing the subject you want to put the subject in context with the environment, 50 mm could be a good option with full frame.
Is there a flash or some other add-on that I should buy that helps the camera? I just had one on board now.
Yes, an external flash is very useful (and two external flashes are better than one). Do not use the built-in flash! It is so close to the lens that the reflections of the blood vessels in the eye produce red eyes. With an external flash, even mounted on the camera, you will not get red eyes (at least a short distance; I have not tested with the maximum power + long distance mounted on the camera). In addition, the built-in flash does not work with physically large large diameter lenses, because the lens casts a shadow. It is primarily intended for the kit lens.
If the room where the portraits are taken has a low white ceiling, an option to make the flash less hard is to bounce it from the ceiling. Requires a flash with a tilting head. But, a much better option is to use it outside the camera, activate it remotely and use umbrella light modifiers.
When selecting a flash, consider its compatibility with the measurement through the lens of your camera, its ability to activate remotely and prefer the flashes that have a fully tiltable head that can be tilted in all directions. Even when used outside the camera, if you shoot outdoors, you may need to tilt the remote trigger sensor toward the camera. Radio triggers, of course, do not have this restriction. In sunlight, you may also want to consider the power of the flash, but in any other circumstance, the power probably won't limit it.