If you are training your puppy for schutzhund, I think crating is important. Your dog has to be in a crate when you go to training and trialling so he has to be used to it. (Your car will not survive if you don't crate)
Crating makes potty training easier, crating keeps your house safe, and I think most importantly crating keeps your puppy safe! Anyone have dollars to spare when you puppy ingests a sock when your weren't looking, develops a blockage, and needs a hospital stay and surgery? Not me. Enjoy diarrhea? Me neither. If your puppy eats something he shouldn't that he found on the floor or in the garbage (at 5 months old my puppy can reach the counter) and his stomach gets upset you could be cleaning up a lot of poop. Do you like yelling at your dog? Cause you'll do it a lot more if you don't crate. My dogs love their crates. It's where they get their best chew toys and snacks. I think it can be more inhumane NOT to crate.
Personally, I don't let our 5 month old play much with our 15 month old. 3 or 4 times a week they run and play together in the field by our house and they see each other through their crates daily when they walk by each other, but not any more than that. They go out separately on walks, we socialize them separately, and we keep them in separate rooms in the house.
I have found this to be important for the puppy because if left to be with the dog, she 100% prefers her brother to people. She comes because he comes and she's glued to his butt, not because she is listening to her handler. So while she's young we're focusing on her handler being the source of all fun and goodness in the world. (Crating also helps with this, fun and happiness begin when you the handler come to bring the dog out to play!!) When we can call her away from play with her brother, then I will know she can be around him more often. Our 15 month old male understands this and will ignore her completely when working. This is what we shoot for.
In Schutzhund training and competition you will work with other dogs on the field and you never want your dog to be distracted by them. So you socialize and train for being "Dog Neutral", ignoring other dogs, they are nothing to be concerned about and they are nothing to pay attention to either.