If you look at the knuckle joints they don't follow a straight line, it runs diagonally on a real hand and helps define the shape, it's also a reason for the extreme flexibility of the human hand. Those skin folds on the finger joints I can imagine would be a nightmare to try and model I think you're doing really well, and I think this project would be a great chance to learn some anatomy. The nice thing is that if you learn humans the anatomy for other mammals is pretty much the same if you stand them up on two legs so it's well worth it.

There's tons of resources for artists online, the largest site is probably www.3d.sk but theres lots of free sites, cgtalk has a whole forum dedicated to this and I'm sure there's a lot of free sites mentioned in the resources lounge here. Also lots of good books that you can get to keep on the side, but you need refs in addition to your own body which is the best resource as you can squeeze and bend everything to figure it out.

I think doing it the way you're doing it by creating one body part and learning the area as you go along is a better way of doing it than trying to memorize the whole body at once because it's difficult and would get dull. But taking a pencil and doing line drawings of the general structure and different poses before adding a high level of detail would save you a lot of time on reworking the model as the base shape need to be good enough to build on. You don't need great drawing skills, it's just useful to understand proportions and shape before modeling and topology. Try drawing a hand it's a lot more difficult than you'd think, do front, side, fist and extended fingers.

The way we learnt anatomy in school was 1) bones, 2) joints, 3) muscle; you wouldn't need detailed knowledge as an artist in the same way you would in medicine, but I don't know a single med student that didn't draw at this point. And once you understand the bony structure, it will make sense how joints deform on a human model and which muscles would be defined because they contribute to specific movements and where skin wrinkles develop and to what extent.