Avoiding aggression in a new puppy

I'm bringing home my first dog soon and my number one concern is aggression.

As a kid, I was charged by a large dog and left with a bit of a fear of them. Hoping to get over it, I'm bringing home a puppy--a golden retriever--to raise as my own. I know aggression isn't a major concern in the breed, but any poorly socialized dog can be aggressive of course.

My grandfather, our basement tenant, owns a terrier mix. He gets along with our cats, but I'm not sure how well he does with foreign dogs. I believe he was well socialized before we received him, but he doesn't get much exposure to other dogs nowadays so I'm kind of scared of how he'll respond. My main concern is that if he does show aggression, I fear that it could have lasting effects on the puppy before he is trained out of it.

I should note that as of this week, I'm in the process of retraining my grandfather's dog--he is 78 and cannot walk him any more, so I've begun to take him in his place. This will include trying to resocialize him, but I'm not sure what to expect as far as that goes. I've considered taking him to our beach front (the closest thing we have to a dog park) to get him used to other dogs again, but I feel like that would be irresponsible as well.

What should be my primary concerns? What countermeasures should I take? Any recommendations?