He needs a complete overhaul of training, lifestyle and management if you really want to make changes. You may be strict with him in some areas, but if he is still jumping on you and putting his teeth on you at this age, he doesn't really respect you.
1) Obviously you have to work, because we all like to live indoors. Think about what this is like for a puppy. He sleeps 8 hours, wakes up and spends and hour with you before you leave for the day at work (if I'm understanding your posts correctly). That means he's spending approximately 10 hours alone sleeping while you commute and work. At 5:30 you need to put your feet up and relax but he has just spent 18 hours charging his batteries with a brief breakfast break and walk in between. You said he gets two walks a day? I'm guessing if one is to the dog park where he runs, the other is around your neighborhood to potty and get out? A walk around the block is good exercise for your 80 year old grandmother, it is not exercise for a healthy golden retriever puppy. It's just not. They need hard, aerobic work that gets their heart rate up for a good 20 minutes and leaves them panting and flopped on the floor for it to make a dent in their energy level. A leash walk is not going to do this. Less than an hour at the dog park isn't either.
Golden Retrievers are hunting dogs, they are in the sporting group and they were bred to run, swim and retrieve game over short distances, all out, with brief rests in between, for hours at a time. We have forced them to become suburban lawn ornaments without giving them a proper job and physical outlet for their energy and mental outlet for their intelligence (Goldens are top 3 smartest dog breeds) and then we don't understand why it's so tough to live with them. I'm not picking on you, this is the vast majority of pet owners. They are smart, energetic working dogs and we expect them to lay around waiting on us to get home and be patient while we perform necessary chores and then behave like model citizens in public till we let them run around for an hour in a stimulating setting. Think about that, it's a huge expectation for a puppy, most adult Goldens don't have that kind of self control. Try to come up with places you can take him to get more exercise. Purchase a 30 or 40 foot long line from the hardware store and clip it to his collar, practice long distance stays and have him run to you for a treat. Get on line and find some videos (Bill Hillman is a good one or Jackie Mertens "Sound Beginnings" DVD is excellent) and teach your puppy a formal retrieve where he returns to heel and wait till you take the ball from him to throw again. Have a special "Bumper" (retrieving toy) that is only used for this exercise. It will become high value to him, it's not used for tug or any other game except retrieving. Eventually you can begin hiding that item in the house while he waits on a down/stay and you hide it. Then you release him to go find it. At first you'll have to help him but it is a great game to get him work indoors when the weather is bad.
So he has all his commands down at home, but he doesn't have them down in public with distractions and excitement. Your next step is to start training him to focus on you. All these things will take time to learn and maturity on his part to be reliable.
1) Is he food motivated? ( I hope so, it makes life easier) Start cutting back on his kibble the tiniest bit and start training him to focus on you in public using food. Pop a piece of popcorn (or a goldfish cracker or a piece of a cheese stick or the best thing is a snack like cheetos, on the potato chip aisle - only they are in the shape of a ball, crunchy cheese balls, ) don't eat it, have him sit in front you and say "watch" or "watch me" and when he makes eye contact with you spit the treat into his mouth. It will hit him in the nose and hit the floor at first but after a while he will get good at it and you can eventually get him to pay attention where you can take a few steps of heeling on leash with him "watching" you and then spit a treat at him. This will eventually transfer out of your house and you can begin practicing outdoors with distractions until you can expect him to start practicing at the dog park. It's a very useful tool. He will learn what "watch" means in 2 sessions I'm guessing. After that, if something distracts him, give him a tap on top of the head with your finger to remind him that he's supposed to be watching you and don't reward him for ignoring you. This will help you keep him under control to listen to you tell him to 'wait' before going through a gate at the park etc.
2) Start having him wear a leash in the house when you are home, about 3 feet long, use it to control him when he acts up. It sounds like you're doing a lot to show him what you expect, since that's not working, it's time to let there be unpleasant consequences to his actions. Absolutely no more letting him jump on you and nip. Ever. Step on the leash when this starts and it will be self correcting. You give him a noise to let him know you're unhappy. "Eh-Eh" in a deep tone of voice - not loud, deep. If he doesn't stop immediately use that leash to put him in his crate for a brief time out to calm down, cover the crate if that helps. Start practicing "nothing in life is free." You can google it and see it's a training protocol for teaching him that you're the one in charge of the good stuff and he has to earn it. You're on the right track having him wait for his meal. Start increasing it by making him lay on a small mat or rug while you fix the meal and place it on the floor next to him and then release him.
A big part of the problem is treating him like a human child with the cooing and baby talk in response to bad behavior. All dogs feed off their owner's energy but a better response would be to calmly crate him when this happens at home and to stand on the leash about a foot away from his collar when it happens away from home. He's not a furry human, he's a dog and he needs to be given more structure. We adjust the way we handle bad behavior with children to different levels of response with a 5 year old or 9 year old than what how we'd handle a 1 year old toddler. It's time to adjust your methods with your dog. You say you've been strict, but it must not be consistent enough or you've set the bar too low. He needs more hard exercise and he needs to know that you're not putting up with his jumping and nipping. Set him up for success, if the curtains are a problem for him, take them down for a few months or loop them up out of his reach. Try rearranging your schedule to get him more exercise that is aerobic and if this doesn't help, I would suck it up and spend the money on having a trainer come to your him to work with you on getting this under control. Make sure it's a trainer who has a lot of experience with large sporting breeds and also has some behavioral training. If you don't he's going to continue to be disrespectful and the nipping makes him a bite risk if he ever gets too frustrated one day. He will continue to get cockier over the next year if you don't make some drastic changes immediately.