I flew solo with DD at 12 weeks, and it wasn't as nearly as bad as it had become in my mind lol We did fly Qantas, but honestly, as I had to hold DD I couldn't manage a tray of food so had to knock back each meal. Maybe I'm just unco but I couldn't work out how to do it. We had the bassinett on the way over (5hrs) and I'd requested it weeks earlier. But I did run into another Mom who had also requested one weeks earlier, confirmed the day prior, and they didn't give her a bassinett seat. None of the people enjoying their extra leg room would swap with her either But I digress, it will depend on the size of the aircraft you're on as to whether they are available.

I did ask at check in if the flights were full, and as none of ours were, they blocked out the seat next to me (I always went window) which gave me a bit more elbow room with BF etc. They make no promises but I found everyone helpful - that was Jetstar and Qantas.

Baby/car seat hire places are pretty common, and most will be qualified fitters. You could organise it beforehand and your friend have it put in their car so it's ready at the airport? Don't know about hiring one straight from a car rental place without the hire of a car. I do doubt it though? Good luck!