I'm tasked with writing a new mixed-use zone for my county. The intention of this zone is not to force walkable communities in the style of NU, but rather to enable more flexibility on lands where we really don't care either way if it's residential or commercial. In our more rural areas along minor highways we have many situations where you'll see "Bob's rummage store" and a residence existing side-by-side quite peacefully. These situations hark back from before we had planning and would be considered non-conforming today. We're trying to accommodate them.
Anyways, to my primary question: Is anyone aware of a resource (website preferably, I'd rather not have to order a book) that lays out the footprint requirments of different commerical uses? We want to allow commercial uses, but we don't want them to be 100,000 square foot Walmarts. The plan is to put a limit on commercial area, but I'm not sure where to draw the line. Rather than pull a number out of my behind it would be nice to have some reality to base it in.
Secondary question: any thoughts or experiences on your experience with such a zone in your community?