There also is a concept out there called inter-planting, or inter-cropping, which is planting placement based on spacing efficiency- planting things with shallow roots next to deeply-rooted things, and making better use of you garden space. I think in the end, I'll probably come out with a combination of both. I haven't made much use of staggered planting dates in the past either, so I'll probably try some of that as well. It's hard, for some reason, to hold back and not start all of the tomatoes or onions at one time.
The in mean time, our seedlings are looking quite good! Most of the herbs are up, the Speckles lettuce is cute and speckled with purple flecks already, and we just potted up the kale today!