I had exactly the same problem with my Milly... she stopped the play biting when she was about 10 months old, but gosh, those first months were long, long, LONG! And pretty painful too.
If it's just play biting, I do think your pup will grow out of it, what's important is not to encourage the behavior, and perhaps encourage him to approach you with a toy in his mouth, or have a toy handy ready to put in his mouth if you think he will bite. If you do get bitten, then stop all interaction. A combination of these two things did eventually stop my pup from biting, but you have to be patient, and constant, and don't expect an overnight result.
As for the collar and harness, I'm so proud of my Milly now: when a friend is watching me get her ready they are amazed, cause she sits on my lap, lifting one paw, then another, for me to slip her harness on, and she's yawning with her eyes half closed as I do it. A harness can be very distressing to a young puppy, but if they're conditioned to accept it correctly, they can associate it with a very calming experience, which is what I tried to create. So I chose something my dog absolutely LOVED (her brush, which makes her relaxed and sleepy and yawny, probably why she yawns now when I put her harness on too!) and used a combination of grooming and treating while I sat with her and the harness on my lap. After she accepted the presence of the harness, I'd pop a leg into it, and then brush and treat some more. Progressing further little by little until she was eventually in the harness, and completely relaxed and happy. Then the next day we would start the whole process over again. It only took about two weeks before she accepted the harness happily without all the brushing between, but I do still treat after putting the harness on every single time (and she still gets a brush while being "dressed" once a week or so too). This is just to reinforce the happy state and make sure she never "unlearns" it.
