This is where I disagree with most of what you have been told, so I will be plain about it. Socialization does not mean letting every stranger and every dog greet your puppy. The American Animal Hospital Association describes the goal as a puppy that is calm and relaxed around people and animals, and specifically separates that from a puppy party.
A dog park is not socialization. It is a room full of strangers with no rules, and for a nervous ten-week-old it can do lasting damage in an afternoon. I have spent a good part of the last twenty years undoing what happened to dogs in one, usually to owners who were doing exactly what they had been told to do. Introductions you control beat introductions you do not, every time.
What I teach instead is distance. Your puppy sits on a bench with you and watches a busy sidewalk. It sees the garbage truck from across the street. It meets three calm adult dogs you have chosen, not thirty you have not. It learns that the world is interesting and that nothing is required of it. That puppy grows into a dog you can take anywhere.
Distance is the whole tool, and it is adjustable. If your puppy is loose, taking food, and looking away from the thing and back at you, you are close enough. If it has gone still, or stopped eating, or is straining to get to whatever it is, you are too close, and the answer is to move back rather than to push through. Working out where that line sits for your particular puppy, and watching you find it yourself, is most of what we do in the sessions outside the house.
I would rather your puppy see twenty things calmly from thirty feet than one thing badly from three. A puppy that got frightened at twelve weeks remembers it, and the fix at eight months costs considerably more than these four sessions do.
The vaccination question comes up every time, and it is a real one. There is no single exposure rule that fits every puppy, and your veterinarian is the one who knows the disease risk where you live. So the split is simple: your vet decides what is safe, and I build the behavior plan around whatever that answer is. Carrying a puppy, working from a car, using your own yard and choosing known dogs all buy you real socialization while you wait.