New puppy, new to breed, need help! Questions

I will start by saying that I was born and raised around pure bred Labs and they are the only dog that I really know their temperament and characteristics well. I have 2 adult daughters, the youngest of which is moving out this coming spring. I am not handling empty nester syndrome well and decided this summer that I wanted to get a working dog when she leaves, I had not decided on a breed, just wanted something for protection and that would allow me to stay active with exercise and training. I met my friends rescue GSD in July that used to be a Police dog in Puerto Rico and was abandoned after retirement. I instantly fell in love with him and decided that I wanted a GSD after my daughter left. In come last week, said daughter comes to pick me up from work and tells me she has a surprise. I go outside my office to a new puppy. Hades is a Belgian Malinois, GSD and pit mix (Mal is mostly dominate characteristics) that is somewhere between 12 and 16 weeks old. He came from an overbreeding situation and him, his brother and parents were left in a camper until they were saved by one of her friends. He got his first round of shots last week but the vet told us not to socialize much until he is all caught up. He seems to be decent with most humans but does not like other dogs at the moment. Now for my questions.

1, He is not a chewer. It could be his age or maybe being new to toys or just the breed. While normally this should be something to be happy about, should I worry? He will chew on treats and bones but has no interest in chewing on his toys.

2. Bonding. I have read a bunch of articles that Mals tend to bond with 1 human and will show favor for that human. I have nothing against this but how do I become a Beta in his pack? Right now when I take him outside, all he does is whine for my daughter. He has severe separation anxiety even when she just goes to the bathroom, labs tend to love everyone so this is new to me. I don't know how to work with him on it or even how to work on his anxiety. She does not want to crate train him which seems to be the only answer I can find online. Suggestions?

3. Energy level. I know puppies sleep a lot but Hades only wants to play and be active for around 30 minutes a day, usually around dinner time. And it is more just jumping off of one of our laps to his water bowl and then back and forth from us to see who he wants to take a nap on. Again, most people would be happy about this but when we try and work on commands he usually just wants to sleep. Could this just be his age? Or maybe that he is not fully up to date on his shots? Could it improve when we are able to start socializing him more?

4. He is underweight, as of yesterday he was an even 14lbs so he has gained almost a full pound in the last week but he is still very tiny and you can see all of his bones under his coat. Are there any better food brands for Mals over others? Our vet suggested trying the Purina Pro Plan instead of Puppy Chow and he doesn't really like it. He will eat it when he is starving but you can tell it is not by choice.

5. Is there anything that I need to know about the breed that may not be obvious to new dog owners?

Thank you in advance and sorry for being long winded, this is all so new to me and my daughter

1) It's a whole new environment for him just give him time he is still getting used to you.
Work with him and he will learn what toys are, most of mine have liked balls/ flirtpoles and some kind of tug to start off with.
Google youtube, there are lots of videos to show you how to teach play.

2) Its not unusual for dogs to favour a certain person.
You will have to build a bond with play, fun training ect.
Quote She does not want to crate train him
If it is to be your dog then it’s up to you how you choose to do things.

3) I wouldn't worry about it, puppies sleep a lot and become more active with age.
It’s also a good idea to have a routine for pup, feeding/ sleeping/ play ect.

4) Purina pro plan has very poor reviews.
https://www.dogfoodadvisor.com/dog-food-reviews/purina-pro-plan-dog-food-dry/

5) Being a crossbreed it’s difficult to tell as you don’t know which genes and traits will be passed on.