what can I expect?

Hi everyone... another post about the new puppy that's joining our family. He is my first GSD, vet estimates btw 5-6 months, and I am curious about how much his temperament will change as he gets older. I've been reading a lot of threads here about young GSDs who seem way more intense, energetic, trouble making, etc, than Cyrus does at this point. I didn't realize til I read it here recently that they can go through a difficult adolescent period and I'm wondering if I should be waiting for the other shoe to drop with him, or if this quiet temperament will stick.

So far, he's very easy. He's only been here a week, and will usually respond to a simple "ah, ah" if he's doing something I don't approve of (setting foot in the bedroom, looking like he wants to chase a cat, heading to the street if he's off lead). He'll run and play on our walks, but in the house is mostly very quiet, will lay and snooze, or cuddle with one of us, or play quietly with a toy. I have left the dogs alone in the house for 2-3 hours and nothing is destroyed or chewed when I come home.

All this is great, I've just been reading stories about GSDs who are much more work, and wondering if you all think he will maintain this chilled out personality as he gets older or if they really tend to change a lot once hormones kick in.

We are going to get him neutered, and I understand that there are different schools of thought about when to do it. I'm thinking to try to keep him intact as long as he remains manageable, and not marking, territorial, etc, and maybe neuter at 11-12 months.

One other question--I've never had a male dog before, so this is new to me! When he gets excited about anything, he gets an erection... I've trained him to sit and wait to go out the door for his walk, and he'll sit there with a big boner! Is this normal? Is there anything I should to about it--try to get him to relax, etc? Or just ignore?

Thanks, everyone, from a GSD newbie trying to learn.