They don't need to have loads of contact with people and other dogs to not be afraid of them. They just need to see a wide variety and to have contact with a reasonable number of 'safe' ones: children who won't squeal in their faces, people of various types (old, young, sunglasses, hats, etc etc), and a range of friendly dogs. they need to learn that their things are not a threat.
What they don't need to do is run up to every person they see and get given a fuss and a treat, and up to every dog they see for a play, otherwise they will learn that those things are super fun and are likely to go on doing them when you're trying to work on recall. And running up to strangers and unknown dogs can, of course, backfire badly - a stranger might kick out at an over-enthusiastic puppy, an unknown dog might bite - in a way that will not help with socialisation at all.
If someone says, 'Oh, what a dear little chap, can I say hello?' it's generally fine to let them fuss the puppy. It's even better if, when the puppy is a little older, this random person insists on it not jumping up before providing attention, and doesn't encourage crazy behaviour. If the puppy is shy and needs its confidence building, I might slip the stranger a treat and ask them to give it to the puppy. If the puppy is a bit too over-enthusiastic, I might say, 'Of course, but let me just get her to sit down first, otherwise she might jump all over you.' If the response to that is, 'Oh, I don't mind!' you need to say that you do, as you don't want this little bruiser doing it to children.
As for dogs, get to know a few local dog walkers. They'll know who the bolshy dogs are that are best avoided, and which ones are likely to be good with puppies. Judge each dog/puppy encounter that you try on its own merits, and be ready to intervene if it looks as if it's going wrong - while, obviously, at the same excusing utter relaxation and a sense of calm!