I just want to start by saying Fritz is super cute, and I am very jealous of not having been through the puppy stage with my GSD, he looks so adorable in the trolley! I haven't been a GSD owner for that long, just 3 months, and we adopted a girl who is 4.5 years old.
There are some things she knows and obviously some things she doesn't. I have no real opinion on protective training, it's not something we plan to do as our girl is not specifically for that, we just wanted to give her the best life possible. I also cannot envision it, with her being so clumsy and happy and bubbly.
She already knows real basics, "sit", "come", "Snowy" (her name), "no" and "this way". But there are things she clearly didn't get taught early and we are struggling to get her to have basic dog manners.
- She was never socialised properly and now she can't be within 20m of another dog without going absolutely NUTS! (Redirection training with high value rewards seems to be gradually working.)
- She never had an authoritative owner, so she is still getting used to doing as we say, she will often bark in refusal of commands. But ignoring her when she ignores us seems to do the trick, although this takes serious patience.
- Some commands, she either doesn't know or doesn't want to know are "Down" and "Wait". This can be really frustrating, especially when meeting new/friendly humans, our natural instinct is to bend down and pet her, but her natural instinct is to jump up and headbutt you in the nose just as you are bending down to pet her.

She's a great girl, we are just getting to know her still, and each week she is seemingly more responsive to us.
Best of luck with the training, and from my point of view, if Snowy could be calmer around other dogs our lives would be SO MUCH SIMPLER!
Best of luck and welcome to GSDHQ! <3