Did I make the wrong choice?

I wasn't sure if I should tag this thread with puppy blues or training help or behavior… I adopted a puppy 6 days ago. She's a 5mo labxshepherdxhusky mix or something like that. She is quite cute and lovable and she learns quickly but I'm not sure if have what it takes to make her a good adult dog. She bites a lot. When she's excited, when she wants to play or chew, she will chew anything that's near her. But it seems like she also bites to show she doesn't agree with the situation. For example, when we leash train and she pulls, I stop and wait for her to settle and come back to walk again. At first she's fine with it but after a few minutes when I stop she jumps on me, nips at my coat, legs or hands or her leash. She also bites/nips when I try to take her harness off when we go back inside.

Shes crazy about my cats. She barks at them and run after them, not aggressively but she's obsessed with them. She will stop mid meal to go after them if they approach her.

Tonight I fed the cats (on the table to give them space from her) and she jumped and started surfing along the table to reach their food. She also often jumps to try to eat my food when I walk with a plate.

All these things separately are nothing much, but all together I find it pretty hard. I had a dog when I was a teenager and when she got older she became a really aggressive dog towards strangers and we had to put her down (this was the 90s and we were first time dog owners). It has been a really tough moment for me and I'm feeling like I'm failing this new pup but I don't want her to grow up to a reactive, aggressive dog.

I now have another dog who's a 9 year old perfect pup, who's a trained assistance dog and I never went through the puppy phase with her, she was already perfect when I got her. The new pup has only met her one day because I share custody of the old dog and she's with me every other week. On the first day they played but the puppy also demonstrated ressource protection with growling and showing teeth.

I'm trying to do my best with this new puppy. But I'm afraid I'm doing everything wrong. I'm afraid she'll snap someone or myself. I'm afraid she'll be uncontrollable. I'm not even sure if I exercise her enough. Sometimes it feels like she's not active enough, other times it feels like she's over stimulated.

I signed up for obedience classes but it only starts in February…

Any help, advice or suggestions are welcome. Please help, I'm so sad and afraid.