I learn best by seeing, so reading helps me very little, but here we go. I start off with basic line art, try doing some detail work, and then end up semi-disgusted with what up looking at because I'm left with these thick black lines cutting through my work. It looks very cartoon-ish. The paintings I've watched on youtube usually just speed through the covering up part, or just don't cover it up. I don't bother weighting my lines anymore either, since I'm going to see them at any rate. I'm using SAI. Please and thank you.
Learn to do other things with your lines so you can get rid of them. Right now you use them to divide sections of you art so it shows shapes.
On a side with shadows it is fine for the lines to be black, because that side is shaded anyway. When there is a side light only hitting on side of the shape it is better if it is the color of that light. If you take out lines then you need to replace them with light and shaded areas.
It looks like your art is heading away from lines, so at some time you might want to start drawing silhouettes and drawing details or draw details until they show you where the edges are. Both ways work, but the second way would be quicker.
Like taking the finished picture and essentially 'dragging' the color over to cover the line? Or would you do it before finishing? Sorry, I just don't know where this step should be in the process.