Honestly, that is not enough information to go by.
Dogs bark at people for many reasons.
Most of them I find are insecurity reasons. The fact that it sounds like it may be getting "worse," is concerning, this is what you said, "Lately with two of my friends its lasted longer than a minute and he went up to them barking, following them barking and it lasted for a few minutes. I crated him right away until he calmed down and then let him back out again, he barked again at him. He kept it up basically and didn't stop, so he was in his crate rest of the time."
Here are some questions to get a better understanding of his behavior:
What is his body like? Tense?
What does his tail look like when he is doing this? (Wagging doesn't mean "happy" just aroused.)
What do his ears look like?
Is he sniffing them and than backing off?
Do you guests
make eye contact and talk to him the whole time? What are they doing?
Does your dog attempt to hide behind you, get to the side of you, in front of you, etc.? Or is he just in constant motion? Attempting to lunge at all?
What are YOU
doing when he does this?
You are the most important part of all this.
More times than not its insecurity. Which is dangerous as insecurities can
lead to fear aggression. So prevention is key before it gets to this point. As he is still only 7 months, there is a lot of time for him to get worse and worse.
From the information that I do have:
Get a dog trainer, one who specializes in GSD's or fear aggression.
Getting him a JOB would help a lot!
You have to be on top of the game. You know when people are coming over, prepare yourself for it. Get your dog on a leash and do obedience with treats as they come in. Taking his mind off of what he is insecure about, and putting his brain to work. Making him THINK, not just using instinct and habit which can worsen and worsen over time to become something extremely hard to maintain.
What it will look like:
Your friends are at the door. (They do not need to knock, you can work on that later, to condition the knocking with something positive as opposed to alerting.) Your friends come in. What you are doing is you are working in the opposite room of where they are. They will sit down on the couch and have a conversation among themselves (this is clearly something you have to talk with them in advance about). Your dog is on a leash in that opposite room with you. You are doing obedience. Sit. Down. Heel. (Heeling is so important for your dog to know!) Slowly. You will work your way into the room with your friends. Your dog should be 100% into obedience and looking for your next command. After, you are somewhat in the room. You will work in a heel. Going past your friends, not stopping, going back and forth. So your dog has to go by them, without reacting. He will be in his working mindset. Keep doing this. Until you think he seems calm and relaxed. Your friends can keep ignoring him. Until you think he is ready for any sort of interaction.
Only you will know how long to do this for, when to stop, etc. As you know him best and no one else is there to tell you how as we are not there with you. Which is why it would be helpful to get a dog trainer.
It may not seem like a huge deal now, but he is only 7 months! It can change drastically. He is just a baby right now!