Yes, that is a great book to get you started. There is a lot to learn but most of the knowledge depends on the abilities of the shop. Everyone has things that work, but a lot is dependent on screens, squeegees, angle, pressure, ink type, garment texture/color, off-contact, flash, print order.... it is one of the most diverse mediums I have experienced. For my first year I kept learning new stuff, but would rarely see that knowledge apply to other jobs.

The photoshop basics are; Select | Color Range... | Select: [drop down] Reds, Yellows, Greens, Cyans, Blues, Magnetas - Then create a new spot channel. Create an action that will do this for you, and in some cases you can Color Range in color mode:CMYK or change hues for better results (30/-30 hue will give you a half step, 60/-60 will change to the next color in RGB).

You can get a good greyscale from color mode:LAB's lightness channel (or inverted for underprints). You can also; Hue/Saturation | [drop down] Master to each of the colors making their lightness dark or light for a nice greyscale (make sure to drop the saturation down on the master before going to the other colors).

After you create these spot channels you augment them with curves and any other photoshop skill that you have to make them 'preview' decently in photoshop (curves, making masks, curves, anti anti-aliasing). I say preview decently because sometimes you have to ignore the photoshop preview from channels and see the art in a 'spot-dimension', imagining it on a shirt in your mind how it may be printed.

I'm still learning but having a lot of fun, it's kind of like trying to solve a cross word puzzle or something. It's difficult to share color separation knowledge because it all depends on the job but if you post an image you'd like to see separated, I'm bored and will run a routine and send it back to you.