Subject: Variables in a Voltaic Pile?

I have several questions at once but I'd really, really appreciate your help. 
You see, I hope to do an experiment to investigate how to produce the highest 
possible voltage from a cell like Volta's Pile and I have the following metals 
at my disposal: Al, Fe, Mg, Pb, Zn, Cu. Instead of using felt as Volta did, I 
intend to use filter paper, yet before I start I'd like to know all the 
different variables that could affect my results. I'd just like some 
confirmation for some of the hypothesises I already have and I'm also wondering 
whether or not certain variables do actually affect the data.
I know that one of the variables is the combinations of metals I chose, and I 
know that the highest voltage will come from a combination of a very reactive 
metal with a very unreactive metal but why?
Also, if voltage = current*resistance, then shouldn't it be that the more 
layers in the pile, the higher the voltage?
Lastly, do the concentration of the saltwater and the thickness of the filter-
paper between the metals affect the voltage? If so, how?
Thank-you very much in advance and I hope it's not too much of a hassle.
- Francesca

Re: Variables in a Voltaic Pile?