I walked the del Norte, switching over the Primitivo in Sept/Oct 2017. So it that is about the same time of year that you are going. It is good you are starting at Grado in September, because many locals go on holiday in October and I found bars and albergues closed. So it is not a bad idea to carry a stash of food, just in case.
I wrote daily blogs about my experience and you can read them here:
https://cathleensodyssey.com/camino-de-santiago/
If you just want to read about the Primitivo, start at Day 21.
A wonderful thing about the Primitivo and doing it in the fall is the solitude you get. Some days I barely saw a soul all day. Lots of time to think and contemplate. Some nights there was only one other person in the albergue. SO, it was a shocker when I arrive in Melide (joining the Frances) and found myself in a 160-bed albergue!
BODENAYA: Don't miss a chance to stay with David at Albergue Bodenaya for a real Camino treat!
RE Hospitales Route: I carried my own pack all the way, but I WAS 63 years old and walking solo, so I was a bit concerned about the Hospitales Route. (One young person said to me incredulously before I left the del Norte, "YOU'RE going to walk the Primitivo???" (I beg your pardon...LOL!!!)) But rumors of its difficulty had me a bit worried, so I had my bag carried around by bag transport for just that one day. It was probably a good thing. Actually the Hospitales is not really technically difficult at all. And there are some beautiful rolling strolls for part of it. BUT, it is a long
etapa with no albergues or cafes. And, the hardest part for me was the cold wind on one of the ridges. If I had carried my pack, I am sure I would have been buffeted about quite a bit. As you will see in the post about it, I was very glad I had taken that path rather than the offered alternative. My experience of the Hospitales is described in this post:
https://cathleensodyssey.com/camino-de-santiago-primitivo-days-26-27/
I am happy to answer any questions.