It's wonderful that so many more people are aware of and are speaking about the importance of socializing their puppies.News is getting out - it is in the pup's best behavioural interest to get him out and about early - before he's had a full set of vaccinations.

There are a few points I want to mention.

#1 Professionals discuss the optimal window of early socialization as closing between 12-16 weeks of age. This does not mean the process stops at week 17.

It means that particular time frame is preferred and has shown to be the time period when puppies have the most success learning (when done properly).
AVASB Statement on Early Socialization - why you don't want to wait.

#2  It's not just about meeting people and other dogs. It's novel sounds, surfaces, locations, people, dogs, moving things, challenges such as climbing over/under/ through, items (umbrellas, walkers, skateboards, lawnmower, snow brush) etc, plus more.....
If you have a summer/spring puppy - bring out the winter coats and other relevant seasonal items. The same is necessary for winter/fall pups. Always expose to the opposite seasonal items.

#3 Socialization is an ongoing process for the lifetime of the dog, especially through adolescence. It's not uncommon for people to stop socializing to dogs once adolescence hits. Behaviour changes and the once social butterfly often changes to a more cautious one.

#4 Extended family members are great but pups need to meet a larger network of people too. Immediate family members are not novel.