My advice would be to get the extra seat. Even if your child sits on your lap much of the flight, you will want the extra room to put down all of the stuff you are going to need for the flight, and it gives you an extra tray table for drinks, etc. That extra room is incredibly important, particularly at that fidgety age.

If your child sleeps in a car seat, I'd bring that, too, unless you are sure your child can sleep in a coach seat. Mine cannot, so I bring the seat onboard when I know she will need to sleep. You don't bring the base - just the seat itself. Make sure you know how to instal it using just the lap belt, and that it's not too big for the seat.

It's possible that you'll be able to use a basinet, but I would never rely on that, particularly for such a long flight with connections. Nearly all children will be too large to use a bassinet at that age - they are really designed for very young infants. You also may get shuffled to a non-bassinet seat, it may not be functioning, or the basinet seats might be reserved for status pax. Also, keep in mind that you can't have the child in a basinet during takeoff, landing or turbulence, so you may need to wake your sleeping child, which is never a great idea.