If you are flying LAX-JFK nonstop in F, you will have flat bed seats, so personal items will have to go up in the overhead for takeoff and landing. You’ll have plenty of room to keep them near your feet for the other parts of the flight if you want. If you’re flying on pretty much any other domestic flight, it most likely doesn’t have flat bed seats and there will be room for your personal item under the seat in front of you as long as you are not at the bulkhead.

Streaming… theoretically yes, AA even advertises this, but in practice it’s far from perfect. You’re better off downloading before you fly, or streaming from AA’s onboard service.