I really need to spend more time on the Camino forum. I checked in a few days after my introductory post and saw that several people had replied to me with some very good advice.
Following that advice, I have booked my flight home so that I will have the longest time possible to spend on the Camino. This does mean that I won't be returning to Paris, but especially after reading about Jo's snow adventures I decided it would be prudent to allow for a few non-walking days.
The trade-off (and there is always a trade-off, isn't there?) is that I will not be able to begin Great Lent at home, or even in an Orthodox parish. There aren't many Orthodox in Spain, and I couldn't locate any churches along the Camino Frances.
I have booked a flight from Santiago de Compostela to London Stansted for February 16, and I will be flying home from Gatwick on February 18. That leaves me with two evenings in London. While there are certainly cheaper places for a stopover, it is a fantastic city and I know that I will not be bored. And I'll get to church each evening I'm there, which is a matter of great joy. I'm rather partial to Ennismore Gardens, but perhaps I should find a parish with services in English.