Your characters are great I'd really like to see them with colour in future. I see your working on your portrait and thats cool as well. I think you are going over and over your stuff again like 'sato' so its probably redundant when I say that
drawing with H pencils is always going to have a lack of tone. I draw with an H pencil first too and then go over the drawing with a 2B and then a 8B. I know how hard it is to commit dark on areas worrying that you might ruin everything and you surely will sometimes, but its worth it for the few that have real depth.
Good luck and thanks for posting.
I think the character designs are tight. Solid balance too. Proportions are pretty damn good. What i would focus on now is your line quality. Seems you might be using a dull pencil. Or at least it's coming off with little sharp decisive lines. More of a build up. Which isn't all that bad, Just come back in a bring some of the heavier contour lines out more, give it some pop.
The direction of you shading is good, going with the direction of the curvatures. If you varied the thickness of your lines you'd bring a new dimension to your drawings. Darker and thicker in the deeper dark areas, thinner and more flowing in the lighter areas.
Good idea with the 100 hands thing. I might join in.
Nice characters. I can already see some definite improvement in your work. The hands are looking nice. I should do one of those 100 of something projects when I get the time. Good luck and keep drawing!
You may want to try drawing some hands from the bones up. Some with just bones, some with just muscle I'm finding its really helping me subconciously place what is happening when I come to draw a figure.