I live near PDX and have seen some shining examples of pods. I am not sure what is involved with your particular city/county regarding regulations, but I can give you a few observations of mine that in my opinion seem have the most potential for success.
Of course, location is key. Also, you want to have a group of vendors that are consistent and professional.
Infrastructure, while costly, is very useful for managing individuals in a pod. For example, having individual meters for each spot helps avoid any complicated energy shortage issues or cost splitting. A freshwater source and wastewater storage and disposal service can be communally covered, but nonetheless is an important part of sustaining a number of vendors in close proximity. Organizing some kind of marketing strategy could be useful for getting the word out about your new community of businesses. I don't think you have to have too many vendors to start strong. On the contrary, I would be careful that you were not so ambitious that you spread a finite amount of gross income over too many vendors. If you are creating something unique in your area, I am sure you will get lots of attention. You can always grow larger if determined sustainable.
Aside from those observations, keep looking up pods in PDX, as there are many. Some doing it better than others. New ones popping up, some going down.