He looks so sweet and innocent. haha.
I thought typical 6 month old brat but I am surprised to read about the pooping in crate. How much time does he spend in it, if you don't mind me asking? Also, do take him to the vet to check out any health problems/ parasites.
As for the bratty behaviour, it is not so much pack leader status as just being a puppy. We worked through this ( and still are at times) when ours was that age with a lot of positive and relationship centered training. It changed the whole dynamics for us. And people now compliment him on how well he is behaved for his age. I would suggest some books: Suzanne Clothier's Bones would rain from the sky, Patricia McConnell's Puppy Primer, and The Other End of the Leash.
And also to practise NILIF. Basically he gets nothing for free.
Nothing in Life is Free
I've come to realise that it is so very important to train them(especially GSDs) without ego. It is all just behaviour and training issues and weeks of asking for incompatible behaviour. For example. if he is jumping or nipping at you, ask for a sit, down, sit and treat him. Then throw a ball. Ask for a down stay. Sometimes I just had mine on leash in the house and sat on the leash so he would have to stay down near my feet with a toy. Also, I started giving him his meals in kongs and toys.
All of this is advice I got on these forums and I am very happy for it.