normal - solid coloring , masking coloring and solid blending (for the area that you need absolute color without confusing yourself)
multiply - mostly i use it as "shadow" layer only but occasionally i use it as soft blender and texture layer
soft / hardlight - I use these layers for ambient lighting , these layers will make the area hue goes toward the color you choosing by the way it's not the main idea of giving the brightness into the area (except you are using the color that really close to white). You may need help from linear dodge on highlight area.
linear dodge - use for highlight it's give very bright light (sometime you may need to lower the brush opacity to avoid too bright light). however the layer may look bright but the surrounding area color will be the same color you are using. So, remember to use the similar color with your ambient light layers.
about recommendation on your work, i think it would be better if i go give you a comment at your page instead.
If it is photoshop i recommended you to stay away from it. It is just the tool that not meant to be use with tablet or freehand drawing.
but if you mean the pen tool on opencanvas it is only one of the brush head that always draw at 100% opacity all the time (imagine the lines of pen in black ink that can't get any darker on the same line not like the pencil that you can keep sketch on it to get it darker)
the always 100% full opacity brush is useful when you want to keep the line look clean and on the same pressure. really useful on inking the manga, cover the sketch lines , create shadows , solid coloring and drawing area for create selection or create mask.
I feel that the example may be a bit complex, given the context. (what you want to share through the tutorial) You explain some basics such as light effects, but other things, such as folds (in a way relevant, since they're distinguished by highlights/shades), although used in a less basic manner, are almost skipped.
But because the light effects subject is really wide, complicate and hard to put in one run. (imagine that i don't cut out the background factor it may require a lot more panel on this tutorial) so instead of teaching the whole basic. This is kinda like a series of technique that for advanced users who can use program like photoshop , sai or opencanvas but don't know that application they are using might have such a potential or useful way to use it. instead of just paint it all on one layer , you can simply paint just basic color and using advantage of retouching to do your work.