The “Junk Copy” step - first things first
Most versions of photoshop are not set up for print right out of the box. Since it works within a digital space it’s output will draw all 4 of the color range of CMYK on all channels, but for PURE black line art it can create either a muddled tone when mixed with color layers, or mess up the effectiveness of your selections.
This is a tip I was advised while working for a newspaper a few years back, and have seen in a few other books about photoshop. Some have a macro to do this but I’d prefer to not repost someone else’s tools. You only have to do this once unless you reinstall photoshop, change PC’s, etc. I recommend using a test image.
If you click on any channel of any image and look at the channel options. If the “selected areas” shows a black box and set at 100 % you can skip this.
Open a CYMK BMP with some black line art on it. Open your channels, and duplicate the black channel and name it Black Copy. On every channel except for the Black Copy - fill with white. Go to the black copy channel and select channel options. If Masked areas or Spot color is selected, change to Selected Areas.
Change the opacity to 100%, and click the color to bring up the color picker. MANUALLY change the CMYK settings to C-0 M-0 Y-0 AND K-100. Hit Ok. This next part will make no sense but hey it’s adobe. Save the document to your desktop as “JUNK COPY” and select TIFF as the format. Close photoshop, delete the junk copy from your desktop, and reopen photoshop. Make sure your channel selection has selected areas 100% black and you will NEVER have to do this again unless you change photoshop versions or computers.