Outdoor veggie and fruit gardeners, how do you protect your crops against disease and from becoming a buffet for pests and wildlife?

I'm growing tomatoes, peppers, and cucumbers for my first time not on a balcony, and I'm a tad concerned about caterpillars, squirrels, and other wildlife finding their way to my crops; that said, I would like to keep my space as earth friendly as possible, so chemical pesticides are out. I've read blog articles about trimming the lowest branches to prevent disease and planting trap crops such as nasturtiums and marigolds to lure pests away from the tomatoes. Do these techniques actually work? How do other gardeners handle this situation?