In July last year I booked my first two nights before arrival. The first so I could take my time and not stress ( I started off injured, so knew I was going to be very slow); the second because I really, really wanted to stay at Bodenaya. The third night was booked defacto -as in, other’s were booking it and I just said - sure, why not.
Nothing more. Zero issues
If you’re at all concerned, look at a couple of the recent threads about shorter stages for the Primitivo ( there’s options for some sections); at the very least, start a little slower and book the first night (Paladin @ 20km, rather than the typical Grado @ 25km- or even Escamplero, it’s just 12km from Oviedo!) then see how you feel.
Yes, there are a couple of stages with no options; but the first ( and the longest) is several days in - the Hospitales. You’ll know how you’re doing by then.
It’s a wonderful Camino, enjoy!