I did an international flight with ds at 12 weeks. It was in three legs of 4 hours -11 hours - 5 hours with 5+ hour layovers between. I was alone. It sucked.
He cried nearly the whole time, and he was a very chilled out baby at home. He was in pain. His ears did not do well.
Sunsequent flights have been much easier, even the way home from that flight was easier. Now he sleeps before we even take off.
I had the basinette from Santiago de Chile to Miami. It was good except we hit a few patches of turbulence and so I had to take him out (when he was finally sleeping) so they could stow it for safety.

I was also assigned an extra seat at the check in desk from Miami to Nwk and the stewardess, who was acting like a BFUAV, took away my faa approved bucket seat "for take off" and then made the executive decision to STOW it below the plane! I don't know why, maybe she enjoys the sound of wailing infants? THEN she had the AUDACITY to ask me to cover up while nursing my child to calm him...I was in the window seat, with no one next to me...because the check in desk had alotted the seat to my BABY!! I was livid (heh heh, obviously I still am, eh?). USair got a long letter from me. I was offered miles but I will never fly them again!
If you have to change from an international to a domestic flight, and you are alone, see if you can get assisstance. I had to collect all my luggage in Miami and transfer terminals...I for one don't think you should be able to put a roof over a sidewalk 4 miles long and call the two buildings one, but whatever. It was torture. I REALLY wished I had brought my stroller! You can gate check it and it doesn't count against your allowances. Great luggage cart if you carry the baby in a sling!
Good luck and try to laugh! So much of the experience depends on the region/country, IME. Latin America was great to fly in: Really attentive staff, snuck families with LOs on before anyone else was even announced, went out of their way, above and beyond to make mom and babies happy. Europe was okay but the closer to England we got the ruder and more aggressive the other passengers were and the less helpful the staff became. Then Scotland was really nice again. The US has always been by far the worst, IME. Other passengers pushing past you to prove they deserve to get on before you, and stewards that seem to hate babies and go out of their way to make you and your baby as
unhappy as possible.
That has been my experience anyway. But I see other people here feel differently.
