I suggest walking from Tui on the Portuguese, Monforte de Lemos on the Invierno, Ourense on the Sanabres, or Ferrol on the Ingles.
- All qualify for a Compostela, if you get at least two stamps per day in your credencial.
- All have adequate accommodations available, especially in the summer months.
- All will have fewer pilgrims on the way towards Santiago.
Of course, this later observation is a relative one. All the routes will be more crowded in July and August as that is the peak holiday months for most Europeans, especially those from Spain and Portugal.
I have avoided listing those 100 km routes that merge with the end of the
Camino Frances. While this is traditionally the 'main' route most pilgrims walk from Saint Jean Pied de Port, it is best walked in the "hip" months of April-May and September-October. The hip months are after the Easter break which always sees a spike in pilgrims, as well as when schools and universities are in session. The latter consideration removes most students and academics from most all pilgrimage routes.
There are likely a myriad of other ways to accomplish this pilgrimage. I am sure someone else will add them here.
I hope this helps,
Tom