Emma Louise, I hate to pour cold water on your scheme but, as far as I know, you will find it difficult to earn a living teaching English as a foreign language.
For starters, you would have to live in a large city, Paris, Marseilles, to find a full-time job. The downside is that accommodation is expensive in large cities.
You'd stand a better chance if you had a teaching qualification AS WELL AS a Celta. I am speaking as one who has TESOL plus a first class honours degree in Linguistics but then I must admit I wasn't really jobhunting!!!
I'm sorry if my answer disappoints but someone or other will be telling you more or less the same thing soon.....
N'allez pas trop vite - Proust