A.F.
I have done this -- numerous times, with baby #1 and baby #2. I wore a baby bjorn and that made bathroom trips EASY :) They came with me. Baby #1 was content to sleep in her baby bjorn for most of the 2.5 hour flights I took (obviously yours is longer). Baby #2 stayed awake the whole time but was still pretty much AOK. Also, I didn't take a stroller until I was traveling with 2 all by myself that were an infant and under 2 years --- I just did the baby bjorn. It minimized the junk I had to deal with at check in or security. If your baby bjorn doesn't have any metal, some of the security people even told me to keep it on going through the metal detector -- mine had all plastic parts and fabric. If you need the car seat, check it at main baggage counter and not at the gate if you can help it and Yes, I would garbage bag it or use something of a heavier duty plastic.
Babies don't get an ear infection, they get swollen ear drums from the pressure and it not being released by sucking or swallowing. As long as you plan on nursing during takeoff and descent (NOT landing) -- you will be AOK. I would say start the feeding session when you start noticing pressure in your own ears both on take off and when descending.
If you are on a bigger plane, they might have a pull down changing table in the plane restroom -- if it is a small commuter jet, they won't. Change the baby right before takeoff to minimize how much trouble it would be to change in an aircraft restroom without a changing table -- yech. *Fingers crossed* you are on a bigger plane. Also, check with the flight attendant at the gate if it is a small plane and make sure you are on the side with the extra oxygen mask -- small commuter jets only have the extra mask on 1 side -- not both so you have to be sitting on the proper side of the plane and sometimes the reservation people mis-book you unknowingly.
Good luck and have fun :)