AA is the marketing carrier, they are the ones responsible for your seat assignments until OLCI opens. The cidesahres between JAL and AA are a bit of a drag in that department.
Jl708 is currently operated with NEO seats, so angled flat. You don't say when you fly, so I did not check if it changes in the coming months.
1 hours is fine for connection in Narita, you only need transit security.
All it takes for JL to check luggage through to another OW carrier is ask them, and bring a print of your ticket. It is a stated benefit that they do it