Peaceable Projects Inc. is a U.S.-based non-profit group that brings the vast resources of the wide world together with the ongoing needs of the people who live, work, and travel on the Camino de Santiago pilgrim trail network in Spain.
There is a similar thread started by Cycle Gal. I recommended Cycling Through the Centuries. I think doing the coastal route would be difficult on bike due to narrow boardwalks. Cobblestones on a bike would be a real test of your riding skills and as Alex says, there are lots of cobblestone paths in Portugal.
I used bicigrino.com on the Frances in 2016 & found the bikes (mtb specialized rockhoppers) panniers & service excellent. They are also affiliated to many bike shops on route. They deliver to your startpoint & you drop off in Santiago. MTB will have no problem on the cobblestone if you don't - I wouldn't fancy narrow boardwalks with walking pilgrims, I'd be inclined to shy away from them as it wouldn't be right to expect them to step off to allow a pass.