It's always nice to see others learning a language and I do have a soft spot for French myself :) A friend of mine is also trying to learn French using Duolingo but I think trying to complement the lessons with a book, as you're doing, is for the best -- I know having a book on Dutch helped me cement some basic things that Dutch Duo lessons didn't explain, so just being able to fall back on it for further clarification is very useful, even if it seems much more advanced than the level we're currently at. Bon courage, alors !