Please don’t despair.
I know where you are coming from as I had the puppy from hell

I had had two working cockers before and thought I was prepared but Maisie was something else. Even at 8 weeks old she was a bolshy teenager

Very bitey and answered back.
At 5 months old I have to admit I hated her and just wanted to go back to the time when I didn’t have her. BUT I felt I had taken her on and she was my responsibility and we would get through things together. I read lots and lots of old posts on COL about the bitey puppy stage and these really did help me as I realized I wasnt alone. I started to take a day at a time and just get through that. Maisie started to get better at 10 months and I know that seems a long time ahead for you but you can get through this stage a day at a time and it may not take so long for you as they are all different. Maisie is still a feisty little girl but that is her nature but she is also incredibly loving and cuddly now too. She is nearly two and a half now and I also have a boy aged 18 months.
Have you thought that maybe you are doing too much with him when out of his crate, over stimulating him? He has to learn to settle himself and if every time he comes out, you are doing something with him, how can he learn to self settle? If he starts to snarl at the lead, just put the lead down until he is calm. It may take many many attempts but gradually he will learn that if he stays calm he will get the lead on and can go for a walk.
Battersea have some good training videos and one teaches how to get a dog to settle. That may be useful to you.
When he has a stolen item, hard as it is, just ignore him. If he thinks you want it, it will make it much more valuable for him. If it is something that you simply have to get off him ( a remote/phone/dangerous item) throw something tasty on the ground and when he releases forbidden item retrieve it. Do you do swapping games with him?
There really is light at the end of the tunnel and you will get there but be consistent and calm with him.
Just to add, it is usually the really clever bright dogs who are the most difficult as puppies
