You do not say if there is a spiritual aspect to your walking the Camino, but if there is, attending the Pilgrims' Mass in the Cathedral would be a not-to-miss part of your pilgrimage. Also, don't underestimate how long you might have to queue in the Pilgrim's Office to get your Compostela or Certificate of Distance, and do try to call in at Pilgrim House where you will make contact with other pilgrims and get advice if needed, plus coffee and laundry facilities.
If you are fit I am sure that you could walk it in 4 days, rising very early each morning, and this would allow you to enjoy the joyful experience of arriving in Santiago alongside others who might want to join you later in a celebratory drink or meal. Don't forget to get two stamps on your Pilgrim's Passport (credencial) in order to qualify for the Compostela. Whatever you do, I wish you Buen Camino!