Can I get away with just one heavy coat?

Yes, provided it is windproof and waterproof. The wind chill in Norway is what makes the cold unbearable, not just the temperature.

Do I really need micro-spikes?

If you are visiting cities like Oslo or Bergen in mid-winter, the sidewalks often turn into sheets of ice. They are small, cheap, and save you from a nasty fall.

How to Pack for a Norwegian Winter

Pack according to the three-layer rule: a moisture-wicking base layer, an insulating wool or fleece mid-layer, and a windproof, waterproof outer shell. You will be layering constantly to adjust for indoor heating and freezing outdoor temperatures.

Select your base layers. Bring 3 sets of merino wool base layers (top and bottom). Merino wool is essential because it stays warm even if you get damp and does not hold odors like synthetic fabrics.
Prepare your mid-layers. Pack 2 thick wool sweaters and 1 fleece jacket. Avoid cotton entirely, as it loses all insulating properties if it gets wet.
Choose the right outerwear. Bring one high-quality, windproof, and waterproof parka. If you are going to be active, pack a dedicated shell jacket and shell pants that can go over your other layers.
Protect your extremities. Pack 4 pairs of thick wool socks, one pair of waterproof insulated boots with a high-grip sole, a wind-resistant beanie, a neck gaiter (buff), and waterproof mittens.
Compress for space. Use compression packing cubes to reduce the volume of your bulky sweaters and parka. Wear your heaviest boots and jacket on the plane to save weight and space.

Can I get away with just one heavy coat?: Yes, provided it is windproof and waterproof. The wind chill in Norway is what makes the cold unbearable, not just the temperature.
Do I really need micro-spikes?: If you are visiting cities like Oslo or Bergen in mid-winter, the sidewalks often turn into sheets of ice. They are small, cheap, and save you from a nasty fall.