Hi Martha! Welcome to the forum!
I walked the Portuguese Central route in 2017 and loved, hopefully I can help with some questions.
You will pass by a fair amount of small cities, so you should not have issues with services such as bars, etc. I have not walked that part, so would not be able to respond properly. There is also the option of taking the train to Valenca at Caminha - it is a 40 minute ride.
There are no climbs at any part of the Portuguese Camino, and going by the coast you will skip the main uphill (Alto da portela), so you will be fine. Look for any place in the Old City when you are in Pontevedra
In Caldas de Reis, there is a tavern downstairs of the main road that is quite old and serves amazing sardines and peppers.
Hotel Moov Centro was excellent, Ibis level but cheaper and in the old city. It was at the top of a hill though, so you may look for something closer to the Clerigos Tower if going uphill is not your thing. Totally worth it to explore the city for a few days, I highly recommend doing a Port wine tasting at one of the wineries across the bridge (in Gaia). Also, try the Francesinha, a local meat sandwich. It is quite something. As well as the amazing cod fish (bacalhau).
Santiago is also worth exploring after you finish. just wander around the city and let the experience sink in - it will be great, independently of what you do over there.
I flew from Barcelona to Porto, and there are indeed many options to fly Madrid Porto for very cheap prices. It is quite easy.
Have a great time, bom caminho!