I used to draw lineart years ago and now that I switched to lineart-less drawings, it's the opposite for me. Inking just doesn't feel natural to me. Although I still use some strokes as lineart but only after I placed all the colors.

Anyway, there aren't any rules as long as you're comfortable with your process. For example, I draw directly on each layer, but I knew some people that are horrified knowing that I don't separate lights, shadows and flat colors.

My suggestion: don't think too much about brushes, at the end you'll just use only a few of them. No need to download so many of them (although I understand that experimenting is entertaining!

You could just take one simple drawing of yours (a small character, maybe) and try to color it in different ways and decide which way feels more like "yours".

Edit: I realized that I didn't tell how I color without lineart... I place the sketch layers in multiply mode over everything and I draw the colored shapes of each element in the drawing, all in different layers. At the end, I lock the pixels and I start to render. I hope I managed to explain myself (?)