Thank you for the tip! I was actually just reading about gearing in an article called "The Art of LEGO Design" (http://cheme.eng.wayne.edu/neuron/LEGO_ROBOTICS/artoflego_ar...)!
Was also looking at Technic kits (such as http://shop.lego.com/en-US/Tractor-9393) with a preference towards those with more pieces, and thus more flexibility.