We have done this and longer flights each year since kids were born so done it with 6mo to 7yo, it won't or shouldn't be as bad as you think, off to a good start with own seat and busy bag - he gets a bag allowance too so make the most of it.
Which airline are you flying with, do you all have the ESTA visa waivers?
Do you have an umbrella stroller? Great if you can check at the gate and have it waiting for you at the door on the other end as otherwise it is a long walk/carry to baggage claim.
Have you ordered childs meal for him? TBH I always order childs meal for myself too then we can eat at the same time as otherwise he might fuss and want to sit on your knee whilst you are trying to eat as they serve kids first unless you think he can eat and then watch a bit of TV.ipad while you eat.
We got ours their own headphones as the ones on the plane are too big for kids and me as have a small head so I have some too we got [[http://www.amazon.co.uk/dp/B0007NWL70/ref=sr_ph?ie=UTF8&qid=1423490985&sr=1&keywords=kids+headphones these ]] as you can limit the volume and they connect to the ipad and the plane. it is so noisy on the plane you can't hear the ipad without them.
Take more nappies and wipes than you think you will need esp on the outbound flight and agree with Meg that you and DS will need a change of clothes. mine puked on me mid flight once, glad I had a clean t shirt to put on.
Maybe take more snacks than you think you will need, often get knocked to the floor etc, small things that take time to eat are good like cheerios and raisins.
Night flight back can be hairy to start off with as they are tired then they serve drinks and dinner before putting the lights out so they can be a bit beside themselves by then. I always take PJs for them so they know it is sleepy time and their favourite cuddly, blanket and small pillow. It gets cold on the plane and they like to snuggle up anyway. Mine always sleep until about an hour before we land which is perfect.
When you get there and when you get back try to get him on schedule as soon as possible to beat the jet lag.
Will come back if I think of anything else or feel free to ask a question.
Have a great time on your trip.