Thanks Often1 and sportsguy1 for your responses!

I checked with AF on bringing the Cosco Scenera NEXT onboard on the specific planes and they confirmed it's OK. Next thing now is figuring out whether that's a carseat we want to use regularly until our Graco 4ever arrives.

In regards to stroller, we're definitely bringing one to the gate. I was asking more about whether to bring the Bugaboo Fox, which is quite bulky, or whether to buy a smaller one (e.g. the Graco NimbleLite or the Mountain buggy nano) and ship the Bugaboo by sea with the rest of the stuff. I'm leaning towards the latter option, I think we'll manage with the smaller stroller for a couple of months, although I'm sure I'll miss the Bugaboo...