Hi, Nauzanplage,
Looking at a map you can easily pick out a 200 km stretch to eliminate. I think people approach this task of Camino-trimming in one of two ways.
Some will prefer to have a "complete" camino, that is, pick the starting point that is 750 or 800 km from Santiago. That would be in the Merida-Caceres region.
Others want to cherry pick a few stages to eliminate the "ugly" or "boring" sections (as you might guess, this is not my strategy
) If you want to do that, though, there is an obvious candidate. Salamanca to Zamora is not, shall we say, stunning. But that's only 60, so you need to find a few more. I think I wouldn't drop anything in the Zamora to Santiago (on the Sanabres) portion. So that means looking for other places, maybe Merida to Caceres.
I think it also depends on whether you plan to return. You could, for instance, do your 750 kms from Sevilla, and then next year come back, finish up into Santiago and then do a shorter Camino, like the Salvador/Primitivo combo, which is one I am particularly fond of! Good luck with your planning. Buen camino, Laurie