Thanks for your reply! 
This would be my first Arduino project yes, though the end product is something I have been working on for months. I'm not expecting to be able to get the scale of array I want, but I'm hoping that with the help of Arduino I'll be able to make a small scale array and learn from my experience.
Correct, the diodes would be somewhat costly. Eventually I'd like to see the diodes mounted on a PCB board as close as possible to each other. Though right now I'm not to terribly concerned with how they are mounted. Hot gluing them to a piece of paper is a possibility at this point.
I'm just curious as to how I could get the readings from each individual diode if there are way more diodes than inputs.