On difficulty, the official stage data give an honest picture. The Xunta de Galicia rates Sarria to Portomarín medium-high because of the climb out of Sarria, and the rest of the last 100 km medium or low, with daily walking times of four to six hours; the full Francés adds the Pyrenees on day one and the El Bierzo mountains, with two weeks of flat meseta between. Pilgrims in their seventies finish every day. The risk is cumulative: 15 mi a day for a month on unaccustomed feet. Training, pack weight, and shoes decide the outcome more than fitness.
On safety, the State Department rates Spain Level 1, Exercise Normal Precautions. The Camino's own risks are road crossings, dehydration in summer, and petty theft in albergues; women walking alone are common, and the existing page on walking the Camino alone covers that. The route is well marked with yellow arrows and scallop shells.
On whether it is Catholic: the Camino exists because the tomb of St. James the Greater was identified at Santiago in the ninth century, the cathedral holds his relics, the Pilgrim's Mass is offered daily at 7:30 a.m., 9:30 a.m., noon, and 7:30 p.m., confession is available in several languages, and the Compostela is issued only for religious or spiritual motives. Churches along the way offer Mass and stamps. Many walkers are not Catholic, and the way is open to them, but a Catholic who walks it with the sacraments in view is doing what it was made for. Whether it is worth it depends on what you bring; the Church promises grace, not an outcome.