Hi, Adi,
Welcome to the forum! I probably can't answer all your questions, but here is a start.
1. Check out these threads dealing with transportation from Barcelona-Pamplona.
https://www.caminodesantiago.me/community/threads/barcelona-to-pamplona.19170/
https://www.caminodesantiago.me/com...e-way-to-pamplona-barcelona-madrid-bil.11689/
I was surprised this summer to find how quickly the trains fill up. Book as far in advance as you can.
If you do a search on the forum, using the box in the upper right, you'll find more threads with info on this topic. For most up to date train info, check renfe.com For bus, check movelia.es
2. There are lots of threads on Pamplona to St. Jean, too
https://www.caminodesantiago.me/com...o-saint-jean-pied-de-porte.34554/#post-316373
3. With 15-17 days you are probably going to have to make some hard choices. I think you are going to have to skip more than SJPP to Pamplona and Compostela to the ocean. There are a few forum members who have walked SJPP to Santiago in 23 days but that's not the usual. Do you have any idea how many kms you would want to walk a day?
Have fun planning your camino, buen camino, Laurie