Any particular reason for picking Estella as your end point (if I understand it correctly)? As someone who broke up my first CF in stages with the intention to come back and finish it, maybe pick a stop with enough connections so you can get to it by bus or taxi wherever you stopped.
I suggest this because we don't know if you prefer to break up the Pyrenees stage into two. Or how many kms you can handle or elevation walk etc. Plus I find if I had a specific stop it makes it easier but often times the Camino takes a life of its own. You might hit it off with folks and decide to stay elsewhere or walk farther. My strategy was to keep my end stage a mystery but keep your departure point as central as you can. May be Pamplona, Estella, or even Logroño. Make it so your first week is one you want to build on, not something you dread coming back to. Break up stages, stop in off-stage stops, and see how your body feels.
If you end up short (or past) your departure point, can always taxi your way to it. I had 3 weeks last winter to start with and I didn't know if I was going to end up in Leon, Sahagun or farther. I ended up in Astorga instead. Give yourself the best flexibility and likelihood of enjoyment. And what you're doing is typical with many Spaniards so you're in good company. Good luck and happy to help further.