I'd just start walking in Irun and keep going for 16 days. You could catch a bus for the stages out of Bilbao and Santander to save you some industrial and city walking, however part of the "camino experience" is the people you meet and walk with along the way, which requires a bit of continuity. In any case the Basque country and its culture are marvellous, and you'll also get to experience Cantabria and maybe even a bit of Asturias. Pintxos, beaches, cider... what's not to like? The nice thing about starting in Irun is you'll have an excuse to come back and finish it the next time you have annual leave.
You don't say where you're from but just make sure you leave enough time to travel back to an airport: some parts of the Spanish northern coast are very rural and getting back to 'civilisation' can be more challenging than you'd expect.