I will address each question one by one for you
CMYK printing is also known as four color process in the screen printing industry. For printing on garments, CMYK is used most of the time to achieve photorealistic screenprinting. with the use of four ink colors (cyan, magenta, yellow, and black). Because these inks are extremely transparent, this process is intended only for white garments because the garment color it self will effect the final screenprint. For example if you were to screenprint cyan process ink on a yellow garment, the print would appear green.
If your design is only a one color image, you would want to create the artwork as a spot color. You mentioned creating a one color image that will be going on either white or black garments. It is very possible you would need to create two different images. One for the white garment and one for the black garment. However if your design is pretty much going to only be text.. Two separate images will not be necessary. Here is an example of how the image created for a white garment would not work for a black garment.
As you can see, the image on the black garment with just changing ink colors, just looks wrong.
The solution here was to create a second image for the black garments, invert the artwork of the dog and create a white outline around the dog.
It is also definitely good practice to get into the habit of creating spot colors as Pantone spot colors.. If you create an image containing the color “Royal Blue”, your idea of what royal blue looks like versus the screen printers idea of what royal blue looks like… could be very different. But if you were to tell him use PMS 287 (which is pretty much a royal blue) , both of you will be on the same page. And by the way.. PMS = Pantone Matching System
Here is some good information about separations you may be interested in
Things to consider: If your artwork is only going to be text, there is no reason you would need to create one version of the art for white garments and one version of the art for dark garments. When artwork gets separated for screen printing, each color of the art work will be its own individual separation. When it is time to output these separations to transparency “film”, it makes no difference what color the artwork is in your image. The separations will always print out as black (whether it is through a laser printer, a inkjet printer, or an image setter).
For your purposes, purchasing a set of Pantone color books is a little overkill I think. In both illustrator and Photoshop, you can load spot colors from the Pantone color books into your color swatches panels. You can color any of your artwork with these Pantone colors.
In illustrator, if you create all of your artwork and every color is a spot color, whether it be Pantone or generic spot color makes no difference.. The separations are done directly in the file itself and when printed, each spot color will print on its own page