Welcome to the forum and congrats on your foster!
My last dog came from a similar situation chained in a back yard with little to no contact besides food and water from 8 weeks to a year and a half old, so I understand having to catch up on manners! If his nose is in overdrive, it sounds like he may work for some nice-smelling food. Positive reinforcement would be a good way to go for a dog that has had a rough start like that. I would start with the basics - sit, down, stay, come etc. If you're not sure about your training skills, you could always hire a trainer to help you out or attend a class.
Shepherds are smart and you can establish some good boundaries early on by being firm and consistent. If he's a bully when greeting people, I would teach him a good sit-stay so you can park him on the floor a short distance from the door when greeting people. Possibly a back up, or a side or heel position for out in public so he doesn't spring ahead to check a person out. If he is persistent, you can physically back him up by just blocking off his path to a person he wants to check out or you can back him up by just shuffling into him.