I think you need to start over. Act like the dog is a puppy and is new to your house. Crate training in an appropriately-sized crate for when you cannot directly supervise potty behavior, and tethering when you can. Take items that are chewable out of his reach and give him dog toys and appropriate chews for his consumption, and praise for good behavior. If he is nipping at people, that is ALWAYS the end of play time with a stern no (I have heard others say you can mimic the YIP or YIPE noise that a littermate would make if a sibling is playing too roughly, but this may be more effective with a young puppy than an adult). I recommend a training program called Nothing In Life is Free, or "NILF". Basically, the dog gets nothing without giving something first. A command to sit, or down, or shake, is given before going outside, before meals, before playing. If your dog does not know these commands yet, you need to teach them as dogs aren't born understanding the words or hand signals we humans use to indicate desired behaviors. I would recommend enrolling in a local basic obedience class where you can take him and learn how to train him gently through positive reinforcement.
You may not have gotten off on the right foot, but that doesn't mean it's too late to change the dog's (and your!) behaviors. Invest in a training class, a crate, and do some research online about positive reinforcement training. I start with treats and then introduce the clicker once the dog understands that treats are a reward. The clicker marks the behavior that I want more precisely than a treat can. So when the dog sits after I say 'sit' or make the hand motion for 'sit' I click immediately and then treat. This way you can 'shape' behaviors, so you are clicking when the dog starts to sit, even if he doesn't sit all the way yet, and he understands he is on the right track.
There are many websites and books that detail this sort of training, so if there are absolutely no basic obedience classes around you can always try a DIY approach but I find for beginners who aren't familiar with dog training that having a mentor to guide them is very useful.
A note on crate size--crate should be just large enough for your dog to get in, stand up, lie down, and turn around. Dogs LIKE small spaces as they are instinctively den animals and do not need a crate that is TOO big, or else it defeats the point of crate training. A dog will not soil where he sleeps, so the point of the crate is to utilize that den instinct to teach a dog or puppy to 'hold it'. If the crate is large enough for the dog to potty in part of it and sleep in another, that is not crate training. Crates should never be used as a punishment. If your dog won't chew it, a fleece pad, blanket, or towel is nice to put in the bottom, but some dogs like the flat, smooth bottom of the crate! Add a safe chew toy for long periods in the crate.
When you are home, try not to use the crate unless you have to--it's much more effective to work on expanding that den sense to the entire house. Tether the dog to you by putting him on leash and hooking the leash to your belt or belt loop. Where you go, the dog goes. If he shows signs of needing or wanting to potty like sniffing around, outside you go! Tell him to go potty or whatever your chosen phrase may be, and praise and treat when he goes potty outside. Then back inside. This will keep him from wandering off and pottying where you don't see him do it. He is much more likely to go in less-used rooms that he doesn't view as part of his 'den'. Keeping him with you throughout the house emphasizes that the whole house is the den and we don't potty inside. If he does make a mistake, clean it with an enzymatic cleaner (it removes the smells that mark that space as a potty space) and watch him more carefully. I tell people, if your dog has a potty accident in the house, roll up a newspaper and smack yourself in the head with it to teach you to watch the dog more closely! Do NOT rub his nose in it or punish him for pottying in the house--he will not understand what that means. Clean existing potty spots with enzymatic cleaner, similarly, because I imagine right now there are places in your house that smell like appropriate potty spots, and he doesn't know that they aren't, yet.
These are the same sort of steps I would recommend to someone who got a new puppy. Just because your dog is older doesn't mean he can't learn how to behave properly. It is a myth that old dogs can't learn new tricks! In some ways, it will be easier than a puppy, because physically your dog has the capacity to hold his bladder and bowels for longer than a puppy can, and he also is probably old enough that he doesn't experience the teething urges that a puppy would, to chew on anything and everything--puppies teethe just like babies and it can be painful and irritating for them, too.
I hope this information is helpful for you and doesn't seem too overwhelming. There is no way to fix things overnight; it is a gradual process, but it CAN BE DONE. By regular people, not just expert dog trainers!
I forgot to mention, that if the dog is not fixed, he may experience urges to mark his territory. Fixing (neutering) male dogs can help cut down on these urges and also can help prevent certain cancers and other undesirable behaviors like running off to find girl doggies in heat. However, neutering a male dog will not automatically make him stop pottying in the house, nor will it make him 'better-behaved'. It simply means he will experience fewer hormonal distractions. Furthermore, dogs have no concept of sexuality or manhood, so you are not depriving him of any experience that he hopes for, nor is the vet taking away something he will 'miss'.
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