I've done QF to Europe twice with my daughter - but at 18mths and 4.5 years.
Some thoughts:
Make sure bub isn't too heavy for the bassinets, regardless of airline. Also request bassinet seat as soon as you book.
If bub uses a dummy, take spares, and pref use a chain to secure it to their clothes. No 5 or 10 second rule with aircraft floors.
6mths will still be all/mostly on milk, if breastfeeding, that's easy, if bottlefeeding, you will need enough formula, etc to cover flights and potential delays. Highly unlikely, but This happened to a friend while on holidays - she got food poisoning on flight, milk supply dried up & had to start bottle feeding.
Take toys/ soft books. Do not expect the airline to have these kind of things.
Take spare clothes for you in-flight. My daughter at 18mths had a huge poo explosion nappy during turbulence on our way to Singapore. I didn't look great for the rest of the trip, but was so glad I had yoga pants to wear rather than the pooed on jeans!
If bub is starting on baby food, various airports may be stricter or less strict on LAGs. At heathrow, the security agent wanted us to open and taste baby food bottles to prove it was baby food (and we'd have to throw it out straight away if we did that). At Venice, we could have walked through with bottles of water as it was "for the baby".
Total personal preference - I would personally go for a sling/baby bjorn to carry bub through the airport, rather than check the stroller at the gate. Depends on how long your layover is, how big baby is, and how long you can carry them for. Other friends of mine prefer to check the stroller at the gate or use the light weight smart stollers (not sure if appropriate for 6mth old).
If driving, I'd hire a car seat locally rather than take it. Bub is better in bassinet if they'll fit than upright in a seat. In my not-so-humble opinion.
