At this time, it is his job to be a puppy, your job is to protect him from strange off leash dogs.
For safer exposure to other dogs, join a training class or a local club. You want controlled meetings with stable dogs for your pup.
This! Absolutely! The only way you can make sure your dog turns into a gentleman is to do lots of training with him. Start with basic obedience and work your way up from there. A well trained dog is the only dog that can be expected to act appropriately in public. The Dalmatian is likely the pet of someone who didn't take time to train their dog.
For now, protect your pup and get started on obedience training.