Yup! Anemone's got it nailed. Start at the beginning of the French Route. Burgos is doable in 10 days. Burgos also has decent bus and rail connections to travel home from.
You might plan to spent one additional day in Pamplona, especially if you are Hemingway fans. You DO know that he wrote his trilogy of books on the Spanish Civil War while living in the tiny village of Burgette (or was it Espinal?), just east of Pamplona. In particular, he loved the trout fishing there.
Similarly, at the end of your walk, in Burgos, plan to spend one additional day there as well. It is a VERY historic city, very key to Spanish history, and El Cid is buried there (the Charlton Heston movie).
More importantly, once you do this first segment, we guarantee that you will want to do more in future. So, starting at St. Jean Pied de Port and ending at Burgos positions you perfectly to return to Burgo the next time to continue on from there, in the direction of Santiago. Many Europeans accomplish their
Camino Frances by breaking it into manageable segments that they return to accomplish each year, until they finish it. As they typically have shorter distances to travel this makes sense.
Since there is no time limit on completing a Camino, in terms of qualifying for a Compostela, and to preserve your entitlement to one, eventually, I recommend you obtain at least one sello / stamp per day starting in St. Jean Pied de Port and continuing until you end at Burgos, or wherever. The sellos should be dated.
All that is required to qualify for a Compostela at present is that you walk AT LEAST the final 100 kilometers of any approved route, AND demonstrate continuous progress in the correct direction. That it might talk you several years to accomplish this is of no consequence to the folks in the Pilgrim Office.
So, let's say for example that you split this up into three of four segments and took as many years to finish. You could still amble into the Pilgrim Office and obtain both the Compostela, provided you walked at least from Sarria continuously, AND the optional Certificate of Distance traveled showing that you walked from St. Jean Pied de Port, 775 kilometers away. The certificate is worthy of framing.
I hope this helps.