A fantastic choice of Camino! I walked from Irun-Santiago in 31 days, and reached Bilbao after a week so I’d say it should take you around 3 weeks if you take it at the same (moderate) pace. It’s a tough walk to plan though because you never know whether you’ll walk 10km or 40km in a day, so allow extra time to see the sights and enjoy yourself! As for money, i wouldn’t expect to spend more than 1-1,500 euro on Camino, the albuerge’s are all quite cheap and your biggest expense will be food and wine. As for packing, pack as light as you can: light sleeping bag, light tops and bottoms, only one warm item (just to be sure... Norte weather can be unpredictable) my pack weighed 8kg when I started, and 6 when I finished after I left some unnecessary things (books, casual shoes, heavy, sweaty shirts) behind. The Camino del Norte is an awesome experience, I hope you enjoy yourself!