Best tool I know for travel planning is to pull out a map and study where you are going. Don’t limit yourself to a tiny GPS based map — get the real thing, unless you enjoy squinting.
Before investing in a set of topographic maps, plan a route so you can buy just the maps you need for the walk. Further planning involves deciding the realistic distance you can cover in a day, increasing gradually from a gentle 15 kms (9.3 miles) per day up to perhaps 25 (15.5 miles) or 30 kms (18.6 miles)per day.
Research lodging options and locations where you plan to rest or explore local culture and archeology. Explore side-trips by bus or rental car if you feel like taking a day or two away from the grind. Although my experience was that once you leave the walking path for more than a day or two, it can be mentally difficult to return to the same level of energy and enthusiasm. This information hub will be helpful to anyone planning a journey on the Camino de Santiago de Compostello.