I have been preparing for the Portuguese route starting in Lisbon also anticipating high temperatures in August/Septemebr. Fortunately our summer was a record for high temperatures, many days in a row in the high 30's. I acted on all the hot weather advice, plenty of water, lightened my load, dampened my clothes, my hair, damped down my arms, good sun hat and sunglasses etc. started early, rests through the hottest part of the day which for us is 1-3pm. I often walked along the coast line and a quick break on the beach, walk into the sea and then set off again. I also noted the dark afternoon clouds and hoped they might rain on me which they sometimes did. Sooo good! On one extreme day I did resort to riding the local bus back to my start point. You will be fine as long as you pace yourself. Your being aware that it may well be very hot is the issue half solved. You will be ready for it and not caught by surprise. If you need to take a ride then that is just fine. It is your pilgrimage and you can do it your way. Keep,safe and happy.