Hi David
Lift passes are the same price pre-booked on when you arrive, just most people prefer to have them organised in advance. A five-day pass is cheaper than five individual passes, but also consider a non-consecutive pass (minimum four days) if you might have a day off from skiing.
The only guiding is officially through the ski school, which we can organise for you in the form of a private instuctor
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Generally the roads are fine and are cleared very quickly because otherwise mountain life would come to a halt - the mountains rely on getting people in and out all the time and for emergency services, so always big effort to have the roads open. The only exception to this is the route in from France by the French border because that road can be particularly be affected by snow and avalanche risk.
When it snows heavily the police set up road blocks in affected areas and you can only pass if you have snow tyres (with snowflake mark) or with chains fitted. Snow/winter tyres are much better because it's not just snow but ice and cold weather, so winter tyres are much safer, although chains will come in handy obviously when it snows.
Hope this helps!
Steve