You are right about getting him used to as many things now as you can, but, you have to weigh the results. For instance, if you throw him in at the deep end, as you say, and he develops some issues as a result, it really hasn't helped.
The thing is, socializing is great, getting him to meet people, dogs, taking him to new places. BUT, you can get him used to other dogs in different ways. For instance, visit a pet store, but stay in the parking lot, and let him watch the other dogs coming and going from a bit of a distance. Gradually shrink that distance, and eventually take him inside.
Or, if you know people with calm, well behaved dogs, you can set up a few meetings. Of course, supervision is key. An older dogs will, sometimes, let a puppy get away with bad doggy manners, because they realize it's a young puppy. But, that "puppy license," as it's called, wears off eventually. So, in the meantime, you want to watch them meet, and if your dog is behaving rudely, immediately remove your dog, and let him observe the dog from a distance.
As Amaryllis said, the dog park isn't for all dogs. You can socialize puppies without going to one.