Thank you very much for the additional information. I really appreciate it!
The important thing...maybe the MOST important thing to remember is that even though I'm sure you already love him...you are a stranger and he is in a strange place, so taking it easy with him for as long as it takes, until he adjusts to you and his forever home. I know that you want to take him out and take him for walks and introduce him to people...but this can overwhelm these unsocialized little guys pretty fast. Imagine if you were dropped in the middle of Russia...you don't know anyone, you don't know the customs, and you don't speak the language...you'd be a little overwhelmed, no matter how nice everyone was. This is what your new dog is dealing with.
I actually have a bit of experience in this situation. I am currently owned by a Maltipoo named Vinnie who spent the first four years of his life in a very small kennel in the backyard of someone who was breeding him to make money. He wasn't house trained, he didn't know how to be a pet and was horribly, terribly skittish around humans. Vinnie showed a lot of the very same behaviors as your Doodle.
With my little guy, the first thing I did was get him a DAP collar to help with his anxiety over the new life he had. These are collars that are impregnated with a man-made version of the dog appeasing pheromone, which is a pheromone that nursing bitches give off to their pups to help them feel calm and secure. It's something that humans can't smell, but it has an amazing effect on dogs with anxiety and other issues. Although you can find them at your vet's office..you can also find them online at places like Amazon.com and Ebay for much cheaper. Just make sure they're DAP brand, as they seem to work better than some other versions.
I'd also get him involved in a basic obedience class. Not because you want him to learn to sit and stay (although that's super nice too), but because these kinds of classes will build the bond between you and your new dog and will help him build self confidence. It will also help him understand that people are okay since he'll be seeing other dogs (whom he likes) interacting with their humans without being fearful. It's good that he likes other dogs so well because dogs always learn faster/better from other dogs. Seeing other dogs in the class not acting afraid may help him understand there's nothing to be worried about.
Almost all breeds of dogs love to have a job, and get a great feeling of satisfaction doing one...what you're going to learn in these classes you can take home with you. Telling him to sit might be a fun thing for you, but for him, it's a job. That will help him come out of his shell a bit.
Finally...make sure you keep all his meetings with new people on his terms for now. If he's timid, allow him to be. Ask new people to avoid looking at him, talking to him, or trying to pet him. For a frightened dog, having someone invade her personal space will be a super intimidating thing. Ask new people to just sit and ignore him. If he comes near them, they can toss him a bit of a tasty treat (My dog loves the freeze dried beef liver you can pick up at any pet store), but not to talk to him or try to pet him. Eventually, he'll associate new people with something good (the treats!!) and will be more likely to want to socialize with them.
I hope this helps...and if you have any other questions about your guy, please don't hesitate to ask.