Sure, fish is fine. Salmon from the Pacific Northwest (I think), however, may carry flukes, which cats can get from eating that fish raw. I can't remember the details, since it's not a concern for me, but I'd do a search on it to make sure you don't give fish with flukes. Other than that, raw...
I usually clip my cats' nails when their kneading starts hurting! Seriously, you'll see how often it needs to be done, cats can vary greatly in how fast their nails grow. With my two, I tend to clip their nails about once a week, or every two weeks.
I'm sure others will have better advice, but for the door thing- my cat just stopped doing it when she got older and realised she's not getting out. I was extra careful when she was having this phase, and made sure she didn't get out (even if it meant having eyes on the back of my head), and...