Actually, that's quite impressive for an 8th grader; it seems pretty well-founded scientifically, too--you're quantitatively measuring potential across a cell. When I was in 8th grade, I probably would have just been dumping different chemicals together to see what happened if I had tried to experiment (fortunately I didn't get involved in chemistry until a few years later).
My only concerns are that if you're doing this on your own that you're safe. Make sure you always wear safety glasses or goggles. I'm guessing your parents know what's going on, but if they don't, make sure that they know and that someone else is around when you're doing experiments. In the case that something goes wrong, you need to be able to go to someone for help if you're hurt.
Other than that, it seems that the chemicals that you're dealing with at the moment are benign enough. I would suggest going to a local university library and check out a general chemistry book. You sound like you'd be interested in the electromotive series, which describes quantitatively how reactive materials are and gives you potentials for different reactions. It sounds like you need a good general chem book, though.