He just is going to need sometime, with your help/interacting with him daily to see we humans are not all bad. He may never want to be held or carried around but most buns don’t anyways. May take him a couple months to relax but in due time the right people will come along and want him for all the right reasons and offer him a forever home. Hope everything works out

I’m sure that as a foster bun he’s been checked out by a vet, but if not, or if it’s been quite a while, I would get him seen soon. His aggression may be health related and you want to be able to rule that out.
Probably litter training would make him happier with his surroundings. Can you get him a softer litter, like Carefresh or Aspen shavings (NOT pine or cedar) so he finds the pan comfortable? Then put hay in one end for him to munch on. Scoop up his poos and drop them in there as well. Set him in the pan a few times and maybe reward him with a raisin for being in it. Soak up some stray pee on a paper towel and put that in the pan too, so he smells his pee in there. He may not know what it’s for, and it should be a spot he likes to be in.
He will probably not like being touched ever as was said. My bunny loves us, but she won’t let herself be touched on her sides, or picked up generally. She is getting better but that’s after 3 years.She growls and lunges, but now it’s as much to play as to be aggressive, so be patient while he gets settled.
Fostering allows you to know a bunny’s personality and be honest with forever home prospective parents. I think of BB’s bunny Vivian, who was unwanted by former owners and not adopted for a long time. But in the hands of experienced rabbit savvy owners, she blossomed. Sterling may need a special person to care for him, but he is cute and loveable and I am sure your work with him will pay off.

And btw, just let him out on the floor and ignore him. Hide treats in your pockets and wait until he comes to you to find them. He will feel safer if he comes to you on his own terms and time.
Keep your palms facing up and fingers closed together when you go to pet him. Gently turn your hand over to pet his head and nose. A hand with spread fingers coming at him from above resembles a bird’s claw, and can be scary.

Poor little guy. He’s going to need lots of time and patience to get used to humans. He obviously needs to learn to trust humans. My bunny Olivia, whom I suspect was either abused or neglected, was aggressive and hated being touched. It took many months for her to trust us at all. The best method was to let her out for several hours in the living room while I read or watched tv. She gradually started coming over and we were allowed to pet her, just a bit at first and very restrictively (for almost a year, we were only allowed to pet her on the nose). Several years later and she will let me lay down with her and snuggle her. She will still honk and hit us if she feels threatened. We only pick her up when absolutely necessary. For run time, we open her door and guide her to the living room.

Sterling (who is very beautiful by the way) is going to need an adopter who understands his situation. I’m sure with patience and lots of kindness he will become a wonderful friend for someone.

Best of luck!