That's unfortunate. It is a ground breaking mod as nobody has really ever been able to make zombies spawn in the map. I hope someone else helps with it because it's very promising. I saw that you said it wasn't meant to be played with the story missions, but I wanted to be able to have all the cribs available and the ability to customize the gang. With all the cribs available, it would have been fun going from safe house to safe house. I also wanted the ability to have more followers and other unlockables you only get by progressing in the game.
As for the food system, would it be possible to have the stamina bar just steadily decrease over time? It'd be more interesting to have more interesting effects like health dropping a bit if hungry, but the steady decrease in stamina would still be sufficient in creating a unique experience imo.
As a side note, I saw that the mod uses some of GOTR. I think a few more things should be taken from it like animations like walking with the pistol, the extra cribs, the extra clothing, more gang options, etc. The more options the better. Even if it doesn't make sense gameplay wise to be able to deck out a helicopter in gold paint, it'd be a nice inclusion to have for those who want to be able to have the GOTR options with the zombies. Maybe also consider changing up the weapons of the saints gang members? In the game they end up carrying AKs and auto shotguns most of the time and that feels a bit weird for a zombie apocalypse. Maybe ditch the auto shotgun, and throw in some other guns like more pistols, the ARs, the sawn off, etc. Basically though, I just wish there were more GOTR features put into it. With more GOTR features, you can experience a more diverse apocalypse. Will you be a basic survivor who clings to whatever weapon you can find as you traverse the city or will you be a special forces soldier sent in to clear out the zombies while decked out in military gear and weapons?
Hope to see more of the mod though. It really is a gem. I always used to try to mimic a zombie apocalypse in the game by doing drunk pedestrains and pedestrian riot. It was the closest I ever got to a zombie apocalypse until now.