Hello and welcome to the forum.
As a sexagenarian, I took 41 days to complete the Camino, starting in SJPDP during Sept and Oct last year. You have picked a wonderful time of year, not too hot or cold, not as crowded, and for me, except for a twenty-minute drizzle, rainless, perhaps because of the drought.
I decided to fly from Miami to Barcelona and then spend four days there adjusting to the time difference and getting over the jet lad. I loved Barcelona. From a central hotel such as the Nisia B&B, you walk to all the main attraction, getting your legs used to hiking. From Barcelona, take the train to Pamplona and then the bus to Roncesvalles or SJPDP. I departed from Madrid, spending three days there to explore prior to taking off. Of the two cities, I preferred Barcelona.
Once on the Camino, you are never really alone. You can hike alone during the day or couple up with others. You can make friends and agree to meet in the evening at a selected albergue or refugio, and then walk at your own pace.
If you use a group to guarantee a reservation, will you be able to adjust the schedule to accommodate time off for injury or exploration or will you have a fixed schedule? In the forty-one I was on the Camino, I could not find a bed in only one town; there was a festival going on and one of the albergues in that town was shut for fumigation. That day we walked a little further than planned, to the next town. I also noticed pilgrims calling ahead to reserve a bed, especially those that taxied their luggage ahead.
You have many options. I suggest make your plan allowing for spontaneity and enjoy the moments on the Camino as they come.
I kept an online journal of my preparations and Camino. If interest, visit
http://www.trailjournals.com/entry.cfm?trailname=11630
Buen Camino.