I think that you're trying to do too much with the Paris side trip. You'll be traveling on day 1, 2, 4, and 8, so you'll only have four days that you're not dealing with airports. Your four hour FRA layover is on day 2, and by the time you get to your hotel in Paris you'll be ready to sleep.

What if you just went straight to Athens, and spend the two nights there? I agree with the previous posters that if you have never been to Paris, the time you have there is not sufficient. Save it for another trip when you can relax a bit and have a few days to enjoy it.