OP I can still remember my first flight with DD when she was 8 months old and it was 18 years ago.
Assuming that you are flying chartered or budget, and there are more than one of you flying with your baby, pay extra to ensure that you are sitting together so you can pass the baby between you. Don't bother with food apart from a quick snack for you, and buy water airside in a sports bottle to keep you hydrated. Have an easy to hand bag of baby snacks, toys and comforters, but not too many.
If baby still takes a bottle or boob then feeding on take off and landing helps with the air pressure (sore ears) and I used to find a dose of Calpol before take off helped, as it made mine drowsy.
If your baby is wriggly then expect to be stood on and squirmed over for 4 hours, I think I got off the plane looking like I had been dragged through a hedge backwards.
We only took an umbrella fold buggy as my main pram was bulky and DD was happy in it.
We changed bedtime to suit us, something that we carried on through our DC childhoods, ours would all quite happily sleep in the buggy so we took it out at night and when they were ready reclined the seat and they slept. We still went to bed earlier than if we had been away on our own, but it was more like 9pm than 7pm. This works for many children but not all, I was away last year with 2 of my DN, both very similar in age, one sleeps 10 hours a night minimum from when he goes to bed, so wakes up refreshed and was not bothered by late bedtimes. The other has a very strict routine starting from getting up at 6am through to be at 7pm or earlier and she couldn't adapt at all and was grisly for the whole holiday. Having said that she is usually grisly so it wasn't a major change from being at home.