there is no substitute for good planning, if you are driving in the north (on any continent!) make sure you have supplies to either walk comfortably for a few hours (warm boots /socks / jackets etc) or enough supplies to camp out in your truck for a couple days. food/water etc. Have twice the supplies you think you might need.!! a small lithium battery booster pack is very useful to have as well. as for oil, 5W040 is sufficient, if you really are concerned about viscosity, you can go to 0W-40 but its not that critical, your engine warms up fairly quickly. when you get underway first thing in the morning, start off slowly, the tires may be frozen square! and the rest of the bushings and suspension will be cold and hard. if you have the air levelling suspension, be cautious in using it, as the rubber in the bags is prone to blow out in the cold! use your parking brake cautiously too, as it is prone to freezing up and staying locked on! (don't ask how I know!) If its at all possible, park in an underground parking lot or covered stall!
make certain that the CCV system is in good repair (as stated earlier) it tends to fail catastrophically in winter!! (the mayo freezes solid) other than that take time to enjoy the northern lights they can be spectacular !!!
best of luck with your trek!

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2003 X5 3.0i (02/2003) sport package, Sapphire black metallic / Black Dakota Sport seats. compass mirror retrofit, trailer hitch retrofit, Prodigy P2 trailer brake controller installed, PDC retrofit, Lumbar support retrofit. heated rear seats retrofitted. Running boards retrofitted and subwoofer install in progress. 4.8is Brakes installed front and back. Bluetooth TCU installed, Rear Fog lights installed. Retrofitted reclining rear seat backs.