Hey Radio_Flyer,
I'm glad you had a chat with your vet, and it's great you're taking him out for long walks, and it's brilliant that he is enjoying them

My aunt's dog is the only dog we've ever known who from a young puppy has disliked walks (he's 4 now) - when somebody goes round in walking boots, or fetches out his lead, he goes and hides in his bed lolol. He does enjoy it when he's out though - and went crazy last winter on a winter walk, there was snow and he loved me kicking snow at him, he was jumping around everywhere trying to catch it, it was hilarious

Whereas my aunt's other dog, who is 14, goes wild with delight when somebody produces her lead, and it's hard to calm her down enough to put it on

I think you're fine taking him for long walks which tire him. When we take the dogs for long walks - though the older dog can't manage it anymore - they always conk out too at the end of it (just like the humans

). And the older dog in the past has managed 20-mile walks even though she's a Yorkshire Terrier, and she's been on long walks all her life, so it hasn't damaged her.
Have you got any teething chews for the dog? I know they're sold and it might discourage him from biting you lol. Make sure they're well-made though and that bits of it can't be chewed off, or if they can, only small bits like bobbles which will pass through the dog.
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She said if he brings me a toy to play with him, don't play. Only play when I give him the toy. Has something to do with dominance. Also, if within a week, or a few days, things don't change, that she would like to see him and work with him.. <<
Yes it is a good idea about the toy. Ben (the 4-yr old) thinks my role is to play with him lol, and in the past when he stared at me (when he wants something he just stares at me, everyone jokes that he is 'communicating' with me lol) I used to give him a toy, but my aunt mentioned a while ago something about it showing dominance, so since then I only give him a toy if I want to give him one, and ignore his staring, which is really funny when it happens. He also stares at me (and at nobody else lol) when he wants something else, like to go outside, or to have a door opened for him so he can get a drink of water, etc

) My cousin says he has me wrapped around his little finger lolol
It's a good idea about your vet working with him, it's a good idea to have somebody else work with your dog. My aunt has been to the local dog school for the past three dogs and when we go there we often take turns in holding somebody else's dog and practising their training. As long as the commands are the same and nothing unusual is expected of the dog, I shouldn't think any confusion should arise. At our dog club there is a puppy class, which is good for socialising the young dogs, because they all need companionship, especially when young, because they can turn nervy against other dogs when older if they're not used to them.
Has he had his vaccinations, btw? I imagine so since you're saying you're walking him, but if not you should carry him until he's had them. When Ben was very young I went on holiday with my aunt and Ben and I had to carry him everywhere (perhaps that's why he doesn't like walking lol, because he preferred a personal chauffeur to using his own legs

) He could catch some things off other dogs (idk what, distemper maybe?)
And you said somewhere about tone of voice being important, and it is. I've taken part in the training of my aunt's dogs and we use a commanding tone of voice for commands - so it sounds abrupt but it shows you mean what you say. A command which sounds like a question will be ignored. You should also enforce it and aim for the dog to respond at the first request - if not, 'help' him to obey by manipulating his body so he does what you say - so if you want him to stand and he's sitting, lift him up by his belly and say 'stand' and then praise him when he's in that position. Or if you want him to sit and he isn't, press down on his rear until he is doing what you want. I'm not sure if it is too early, but are you trying any training when you're out on his walks? Eg walking him to heel? Another good training thing which comes in useful on walks is training the dog to recognise arm signals when out walking - dogs often run in front and sometimes don't know which path to take when it splits - and you stick out an arm and the dog knows you're doing that way and so can take that path. I don't know how my aunt got the dog to understand that though, I can ask if you want.
Like others have said there will be lots of info online on training dogs and looking after puppies, there will be info in your library too, or you could buy yourself a book which looks good so you would have a reference guide at home. My aunt has mentioned (or I've read somewhere) that often it's not the dog's fault for 'misbehaving' when training, but simply through him not understanding a command. Not saying that that is applicable to you, but it is useful to keep in mind if your dog seems to be disobeying you when you're trying to teach him something new.