The main reason for a legroom seat is that you won’t have anyone in front of you lowering their seat on you, and that for me is a massive plus. Also you have the freedom to get up, stretch your legs as much as you want.
Nobody above the age of 5 changes into a PJ. Have loose pants. I travel with Birkenstocks because I like to remove my shoes during flight and it is quick and easy to put them on to go to the toilets or walk around. Toilets can get quite dirty after a bit and you don’t want to step on urine in your socks.
On longhaul flights, the overhead bins are massive, plenty of space for your bags. If you are window there is a side pocket on wall. I don’t really need stuff from my bag.
Have a look at the special meals section if you have dietary preferences. I always pick the fruit platter if available. A special meal is delivered before the general meal service, and this means you also have the tray out for longer.
Many airlines have a snack tray in the main kitchen and you can ask for a drink at any time in the main kitchen as well. It is often at the back but not always .
Have a pen with you because you will have to fill a form for custom before landing.
DO NOT BRING ANY FRESH FOOD. Leave everything in the plane. Be it a forgotten apple at the bottom of your bag or a half eaten sandwich. Massive fines for fruit, veg, meats, …..