Advice for a trip abroad please.

[Talen84]

I'm after some advice please.

Next March I am going on holiday to Northern Finland, mainly to try and see the Aurora. I am planning on taking my camera with me, but having never flown (with or without camera) or used any photographic equipment in the sort of temperatures I'll be in I'm not sure of how best to go about various things.

The temperature range is likely to be around -4C to -15C (day/night averages.) Obviously this will have an effect on the batteries, so I'm planning on taking as many as possible. However from reading the rules regarding air travel I suspect I will only be able to take 3, one in the camera and two spares. Should I consider a battery grip that I can fill up with alkaline batteries as well as my normal Lithium batteries?

Another consideration is how best to transport the camera (hand luggage), currently I have a fairly small Lowepro Nova 160 case which fits my camera and two short lenses (18-55mm and a 10-22mm) but doesn't have room for my 100-400mm. What case would you recommend for the above lenses along with a Canon 550D, spare batteries, memory cards, a few filters, remote trigger etc?
I think my tripod will most likely have to go in the hold, well packed in the middle of my suitcase.

Is there anything else I should be thinking about for photography in adverse conditions? (I'm aware of condensation problems going into or out of cold weather.)

Thanks in advance.