Dear KFrances, it tugs at my heart to read posts from first-time pilgrims getting ready to go to the Camino, worrying about albergues being full. I know it can be difficult to feel at ease about something when you haven't actually been there yet and experienced it. But please know that all is well and you need not fret.
I have walked the Camino Francés four times, twice in September-October, and twice in June-July. And I'm set to walk again this year, in July-August. Of the four times I've walked, only once have I arrived at the albergue where I wanted to stay and found it full. I think those are pretty greatly super odds!
(And the time the albergue was full was in Ferreiros, a teeny tiny place after Sarria, at 7:30pm! Of course there were no beds by then!) But my friend and I could have stayed in a farmhouse just down the road from there that had space, though we decided on another adventure and continued on to Portomarin where there were still plenty of beds available at the municipal albergue.
Albergues do fill up, but the chances of you ever needing to sleep outside are slim to none in my opinion (and experience). The night I stayed in Tosantos in 2011, the place was technically full. But when I woke up in the morning and went downstairs I could see that the hospitalero had rearranged the furniture in the reception area and there were 4 or 5 pilgrims sleeping in there on mats, and a few more in the entrance hallway. In 2012 when I slept at the monastery albergue with the nuns in León (my fourth time staying there), there were extra mattresses all along the corridors downstairs and outside in the courtyard and entryway! And again in 2011, on the way to Negreira (walking from Santiago to Fisterra), there were 5 pilgrims sleeping in the dining area (and in 2015 it was the same). Kindness makes space.
Ponferrada is a beautiful place for you and your husband to start your Camino! You'll have a lovely time getting conditioned on the way up to O Cebreiro. You'll get to experience the rascally short steep climb to Alto do Poio!
And there will be plenty of possible places for you to stop and sleep for the night. It's summertime, so you'll likely want to start early in the morning to beat the heat (though once you're in Galicia it's cooler, which is lovely). Stay aware of how you're feeling (maybe you'll feel inspired to walk a little longer than you'd planned, as you get into your Camino rhythm), know that you can stop earlier if you want to, and know that there will most likely be beds wherever you're thinking of staying.
Last year I was full of energy and walking healthy and strong (I learned a lot about physical limitations and also shattered a lot of mental beliefs about what I thought was possible, a valuable gift and life lesson for me), and I walked from Ponferrada to Santiago in 5 days (my first year I did it in 10). So your 17 days should serve you well and really allow you to savour the experience with plenty of time.
Buen Camino! I wish you countless blessings on the Way.
Rachel