I don't know when Seth's route will be released. It's a bit emotionally tough as it deals with recovery, but I do plan for it to come out. I am working on completing the Story Mode char's open mode routes for the time being, but Seth will be released.
Sterling's route is short so don't get too excited. It's accessible through Dallas' route. There will be an option to stay with Sterling or go after Dallas, you must stay with Sterling.
If you want the cheat codes, email me: maselphie AT gmail