Steve, thanks very much for your feedback! I have a couple follow-up questions...
sdturner:
however the Arduino can't supply that kind of current. You will need a seperate voltage supply. One motor can draw up to 430mA. Multiply that by 4 or 5 and that is a lot of current.
Admittedly, I am very new to these things so I might have a misunderstanding, but based on what I've read I was under the impression that one of the functions of a transistor is to allow a high-power device (like a DC motor) to be able to safely draw more current from a relatively low-power device (like the Arduino). Or am I confusing things?
sdturner:
Also the motors will probably be pretty noisy, so it would be better to seperate the motors' and Arduino power supplies.
Hmm, interesting point. Would there maybe be a way to prevent any noise from the motors from affecting the Arduino? If I recall correctly, I think I've seen circuits described that have safeguards in place (e.g., diodes and/or capacitors) that prevent noise from a motor from affecting the Arduino. Any thoughts on this? Or is this not really an option since I'll be using multiple motors (i.e., just too much noise)?