Hola
7 weeks. Perfect.
Because in other words, you don't have to worry about your home ticket at all.
Of course no one wants to throw away money on expensive tickets, but in my experience it is impossible to predict whether it is cheaper to buy now, a bit later or just before returning.
Once you arrive in Santiago, there will be plenty of options with bus, train, rent a car, air, walk some more... I can't imagine the extra cost, if any, will be more positive than starting your Camino and once you know it is over, then find your transportation to wherever you want or have to be.
Also, many pilgrims don't make it to Santiago because they are injured, tired, bored, emergencies at home, etc.
My advice is to start your Camino and take it a day at the time. If possible.
Try not to plan to much ahead.
Buen Camino
Lettinggo