Rumme, I was perusing the zone 7 map and that covers almost all the southern states plus the western states and zone 7 (yellow) even goes up into northern Canada. Where you are in zone 7 will help determine if tilapia will overwinter or not (probably not if the temperature can get below freezing at times which zone 7 can.
However since your goal is to eat out of your pond then tilapia would be great as they offer themselves up for harvest every year precisely at the same time. It is a little late as your pond is dug but some advance planning would have given you opportunities to make it easier to capture the tilapia at the harvest date.
If you want to eat crayfish, the southern states seem to have a limitless supply of large crayfish and even sell them by the 15 pound bag at local markets. If you have shelter/cover for them in your pond a sustaining population can be had.
I have no experience with mussels or crabs.
If you are in the south (georgia, texas) heat can be an issue in a small pond. Aeration might be mandatory.
