No, it's unlikely that the issue is with the heroes. Just try tweaking the settings.
And yes, I'm not sure if the city selection works in single-player. Try launching it from the multiplayer mode (there's a checkbox there that says "display single-player maps" or something like that).
Regarding crashes caused by scripts, it's a known issue. But your quests don't need scripts. I'm saying that the FAQ should have information on how to create them in general.