Hi, Beatrice,
Good to hear from you again!
Assuming you don't want a repeat, you are looking at caminos like the Mozárabe/Vdlp/Sanabrés or some of the many wonderful solitary routes like the Ebro/Castellano-Aragonés, Lana, or Sureste/Levante. To get into Santiago starting at the Mediterranean, though, would push the total higher than 1000. Is ending in Santiago important to you?
The Olvidado from Bilbao to Ponferrada and then the Invierno from Ponferrada would be a good choice, but that probably doesn't reach your target kms, so you could start back further on the Norte. Same for the Labañiego plus Vadiniense into Mansilla de las Mulas. Have you seen Ray y Rosa's map? It is a great schematic and I think it's the most complete. It's on their website and can be enlarged by clicking. It has a huge watermark across it to prevent printing, but you can see all the options in one place right there.
http://www.rayyrosa.com.
One other choice, a route I really liked was the St. Jaume from the French border on the Mediterranean (Llança or Port de la Selva to Montserrat) and then on the Cami Catalá through Huesca and on to the Aragonés. That is one gorgeous route. Again though, you're looking ag way more than 1000 if you want to get all the way into Santiago.
Have fun planning, it's one of my favorite winter activities! Buen camino, Laurie