Oh sod the English speaking community!
Steer clear from the British ex-pats and get stuck in there, the best way to speak French is to immerse yourself in it. Trust me, you won't be too far from the odd ex-pat anyway, you never are in France.
We lived there for a while too. Had the BEST French neighbours and loved everything about France. But as your mind will be preoccupied with the best bits, here is what you really need to know:
Renting or buying a house is full of red tape, very confusing and a bloody nightmare. You will need a translator to interpret the documents for you and to need to make sure you know exactly what you are letting yourselves in for.
Getting registered in France for benefits/tax/whatever is also a very long and protracted road and unlike the UK, translators are not provided on tap.
However you will meet many very helpful French people who speak English. On the whole the French are exceedingly helpful and will go out of their way for a neighbour.
If you intend to have kids, your pregnancy and birth will be under the hospital's control, down to the very date you give birth. You don't really get to have a say. This is a country which thinks that home births should be prosecuted.
They love their dogs.
Food is quite expensive now. You can get more or less everything you need from the supermarket but French markets are better, however they are also more expensive.
I would recommend you take a crash course in French before you go and then learn whilst you are out there. It will take time and you'll have days when you feel like just giving in, but don't. It may well be the best move you ever made!